Advanced Lithographic Micro Photo Electroforming

pushing the boundary of high precision metal manufacturing

Electroforming process
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The Ultimate Intoduction to Electroforming

1. What is Electroforming?

Introduction to Electroforming

electroforming depositionElectroforming is a metal forming process by means of electrodeposition, similar to Electroplating and Electrorefining. The electrodeposition process takes place in an electrolytic bath and involves two electrodes (an anode and a cathode) and an electrolytic solution. The mandrel is placed in the bath and the electrodes pass a DC through the solution. The DC converts metallic ions into atoms that are continuously deposited on the conductive areas of the mandrel until the desired metal thickness has been achieved.

Compared to other traditional metal forming technologies, for example casting, forging, stamping, or deep drawing, Electroforming can deliver mass volume at superior accuracy and extreme design complexity, due to the fact that it can replicate the shape of the mandrel at extreme accuracy.

Electroforming is also an additive manufacturing process specialized for the production of high precision metal parts. Its uniqueness is that you can grow metal parts atom by atom, providing extreme accuracy and high aspect ratios. Typical precision of a electroformed part goes down to 1 to 2 μm, which is beyond what most other manufacturing technologies can reach.

Veco, as the world leader and largest independent supplier of Electroforming, has been moving the industry forward, with unparalleled experience of Electroforming, advanced lithography technology, and accumulated knowledge of metallurgy. Veco’s unique Advanced Lithographic Electroforming, also referred to as Advanced Photo Electroforming, is predominantly done with nickel, followed by palladium nickel or copper, depending on specific demand (learn more about materials).

From traditional Electroforming to Advanced Lithographic Electroforming

Photolithography refers to the process where a geometric design pattern is projected to a photosensitive resist on a substrate by the means of light. Traditionally, this is done by placing a mask on the photoresist layer and exposing light to the entire mask. Laser Direct Imaging is the next step in the evolution of the Photolithography technology. 

As the world leader in Electroforming technology, Veco is the first in the industry to apply the advanced Laser Direct Imaging technology in high precision metal parts manufacturing. At Veco nowadays, 90% to 95% of our photolithography process is done by Laser Direct Imaging. The combination of LDI and our leading Electroforming technology has enabled us to further push the boundaries of the industry with our Advanced Lithographic Electroforming, providing our customer with high precision metal components in higher quality, at lower cost, and with quicker turnaround.

(1) higher quality

Higher resolution (between 25.400 and 63.500 dpi) is possible with LDI, which is beyond traditional film quality and can potentially replace glass masks. 

Moreover, In case of multi-layer electroforming, the second/additional layer needs to be perfectly aligned. Doing this manually is inaccurate and time consuming. With the Laser Direct Imager, perfect alignment can be done automatically and efficiently.

(2) lower costs

Laser Direct Imaging (LDI) is a maskless photolithography technology. Compared to the conventional way that needs a mask for exposure, using the maskless photolithography process means reduction of the costs of glass masks. One such mask costs around 5000 dollar.

In product development and prototyping , it is common to have corrections or different versions of product designs, which means more masks will be required, and more costs involved.

(3) quicker turnaround

The elimination of traditional masks in the procedure not only reduces tooling costs, but also reduces lead time.

Production of one mask needed takes up to a week, and when there’s corrections the procedure needs to be repeated again. With maskless LDI, on the contrary, corrections can be processed immediately in the next exposure. The LDI  is capable of projecting high resolution images directly from a CAD file, thus allows fast and easy adjustments to be done to new photoresists. 

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Electroforming process overview

Electroforming process

Veco’s Advanced Electroforming process is a unique combination of unparalleled industry experience of Electroforming, advanced lithography technology, and accumulated knowledge of metallurgy. It comprises 6 steps.

1) Cleaning

A metal sheet substrate is cleaned and degreased.

2) Coating

The cleaned metal ‘blank’ is then coated with a light-sensitive photoresist.

3) Exposing

The metal sheet is then exposed to ultra-violet light, which hardens the photoresist.

4) Developing

After the image is transferred by UV exposure the substrate is developed, rinsed and dried.

5) Deposition

An electrolytic bath is used to deposit metal onto the patterned surface.

6) Harvesting

The electroformed part can be harvested from the mandrel, once the material is plated in the desired thickness.

7) Inspection

Full inspection by experts.

Types of Electroforming

At Veco we offer 3 types of Electroforming: Electroforming Overgrowth, Electroforming Thickresist, and Surface Replication with Electroforming.

(1) Plating Defined Electroforming: the Overgrowth Method

Plating defined electroforming is also referred to as an overgrowth method.

Fig. cross section of an overgrowth product.

It uses a thin photoresist pattern to shield parts of the conductive substrate. A light-sensitive coating is applied to the conductive surface, and it will polymerize where it is exposed to UV light. Metal grows over the photoresist and the thickness of the product  exceeds the thickness of the photoresist, hence the process is also known as overgrowth. Note that outer corners will round off during growth, while inner corners will be sharp.

The process is mainly used to make sheets with small conical orifice s for filtration and (ink)jetting. 

(2) Photo Defined Electroforming: the Thick Resist Method

Photo defined electroforming is also called the thick resist method.

Electroforming hole

Fig. cross section of a hole made by thick resist

In some cases, it is desired to make the product thicker. This is when the thick resist method is applied. A thick pattern of photoresist is used during photo defined growth, such that the thickness of the product  does not exceed the thickness of the photoresist.

Aspect ratios  up to 1 can generally be achieved with ease. The exact limits depend on the size and geometry of the products .

(3) Surface Replication with Electroforming

The electroforming process allows for extremely precise duplication of the mandrel.

Fig. Example of surface replication by Electroforming

Fig. Example of surface replication by Electroforming

 The high resolution of the conductive patterned substrate allows finer geometries, tighter tolerances, and superior edge definition. This results in perfect process control, high-quality production and very high repeatability.

Electroforming is therefore perfectly suitable for high precision surface replication at low cost and in high volumes.

Benefits of Electroforming

1) Cost reduction

With Electroforming, there isn’t substantial investment on equipment to start a production. This makes Electroforming cost effective from prototyping to mass production. With many manufacturing techniques, you’ll need additional tooling or machinery before you can start the process. Take die-cutting for example a punch will be required to invest before production can be arranged.

With many other metal fabrication methods such las laser cutting or milling, every piece is handled one by one, resulting in longer lead time especially with larger volumes. Electroforming on the other hand allows you to simultaneously grow a large number of high-tolerance parts in one go, which makes it very suitable and efficient for large volume production. Production cost can therefore be reduced from volume production and efficiency improvement with Electroforming.

2) Perfect replicability from prototypes to mass production

The electroforming technology is known for perfect replicability and reproducibility, due to the fact that the process allows for extremely precise duplication of the mandrel. The high resolution of the conductive patterned substrate enables finer geometries, tighter tolerances, and superior edge definition. This results in perfect process control, high-quality production, and very high repeatability.

With metal fabrication methods like Milling, the machine needs to mill every piece one by one, which directly affects the time that is required to produce larger volumes. This is also the case with many other processes like laser procedures: every metal part needs to be individually cut out. Electroforming on the other hand allows you to simultaneously grow a large number of high-tolerance parts in one go. The more metal pieces that are needed, the more interesting electroforming becomes.

Electroforming is therefore perfectly suitable for high precision surface replication at low cost and in high volumes.

3) High-precision metal parts

With the trend of miniaturization, manufacturing industries see an increasing demand for metal parts of very high precision. In the new generation of production development and design, components at micron or even submicron level are in the demand— demand that conventional techniques such as laser cutting or stamping can’t meet.

Electroforming in combination with advanced lithography process can be the technique to meet the demands of miniaturization by providing the next level high-precision sheet metal parts. With Electroforming, high precision sheet metal components can be made with extreme accuracy. The standard deviation of most critical feature can be only ~0.1 µm on one single part.

4) Freedom of design

The process of manufacturing high precision components straight from CAD design files is an obvious indicator of freedom of design. Without large investment to start production, Electroforming can be used for fast prototyping or mass production, or more ideally both.

Electroforming is thus very suitable for the future-proof experimental approach for next generation of product design and development: a design method where various versions of component designs are made to see which one works best. Instead of using different manufacturing method and handling with multiple suppliers for different components, Electroforming can be the one stop solution for different designs from prototyping to industrial production.

5) Short lead and delivery times

With Electroforming, short lead time and delivery time can be realized. Compared with other manufacturing technologies which requires more time consuming processes, Electroforming process is much more time efficient. In stamping, for example, a die may take up to months to build. In CNC Punching, a die is available within days to weeks. After that the realization of the die, the creation process is yet to be initiated. A mold that is used for Electroforming, on the contrary, can be produced within hours with the Laser Direct Imager.

Electroformed components can therefore be created and delivered within 3 weeks — and usually even sooner, depending on the complexity of the project and co-development procedures.

6) Multi-layer structures

Electroforming is not limited to producing 2D structures because additional layers can be grown by repeating the deposition process. These additional layers can reinforce thinner electroformed parts, making them easier to handle and less fragile. Moreover, these additional layers can be grown in different directions, which can provide more delicate structures to meet complex design and functional demand. The multiple layer capability brings new possibilities for many industries that demand complex precision metal solutions

7) Straight side walls, free from burr or stress

With Electroforming perfectly straight side walls can be achieved with no burr or stress, which is important for many components. This demand is hard to be met with other techniques. With traditional laser processing methods, for example, you will often end up with side walls that are relatively rough on the edges due to heat influence.

8) Special conical hole shape with non-clogging benefits

Electroforming allows you to manufacture components with very unique conical hole shape. This enables us to provide high performance filtration sieves with self-releasing advantage, the filter won’t easily clog and stays clean for a longer use.

Besides filtration the unique conical hole shape sees applications in various industries including medical. Our Electroformed nebulizer nozzle plate plays an essential role in the state of art nebulizer, releasing millions of micron-sized droplets per second through its unique geometry, forming a perfect fine mist for targeted delivery to the lung.

9) Alteration of material properties

Electroforming allows for alteration of material properties, so different material properties can be achieved with the same material. When altering material properties doesn’t suffice, for example if high corrosive resistance is demanded for special application, or a particular material is necessary to be in contact of human skin, that’s when coatings comes in. A layer of material such as palladium or gold can be coated followed by Electroforming process.

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2. How does Electroforming work?

Advanced Lithographic Electroforming Step by Step

Veco's Advanced Lithographic Electroforming process is a unique combination of high precision photolithography and electrodeposition based Electroforming.

1) Cleaning
Electroforming process - cleaning
A metal sheet substrate is cleaned and degreased.

2) CoatingEF_coating
The substrate is coated in a light-sensitive coating/photoresist.

3) Exposingelectroforming process - exposure
The substrate is exposed to ultraviolet (UV) laser direct imaging (LDI), whereby the CAD part pattern is projected and transferred onto its surface. The resulting patterned surface is split into conductive areas and non-conductive areas by the photoresist material hardening in the latter.

4) Developingelectroforming process - developing
The patterned substrate is developed, meaning the unexposed photoresist is removed to expose the conductive areas. It is then rinsed and dried. The patterned substrate is from here on referred to as the mandrel (part model).

5) ElectrodepositionElectroforming process_deposition
The electrodeposition process takes place in an electrolytic bath and involves two electrodes (an anode and a cathode) and an electrolytic solution. The mandrel is placed in the bath and the electrodes pass a DC through the solution. The DC converts metallic ions into atoms that are continuously deposited on the conductive areas of the mandrel until the desired metal thickness has been achieved.

6) Harvestingelectroforming process - harvesting
The electroformed part is harvested, or separated, from the mandrel. The electroforming process can be managed in different ways to achieve different product features. For example, if a thin photoresist is used and the metal is allowed to grow over it, resulting in the thickness of the part exceeding that of the photoresist, the outer edges will be rounded and have a bell mouth shape. Alternatively, if a thick photoresist is used and the metal is not allowed to grow over it, resulting in the thickness of the part being less than the thickness of the photoresist, the outer and inner edges will be straight and sharp.

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Table of Contents

material properties

Typical materials we offer for Electroforming are Nickel and Copper. Whereas we have a variety of nickel types available with different material properties:

  1) Veco84  
  2) Sulfamate
  3) Meta
  4) Hr-Ni
  5) PdNi (Biocompatible)

electroforming material property

 
 
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design guideline

(1) Plating Defined Electroforming: the Overgrowth Method

With Plating Defined Electroforming, metal grows over the photoresist and the thickness of the product (T) exceeds the thickness of the photoresist (TR), hence the process is also known as overgrowth.

Plating defined Electroforming

Plating defined Electroforming

(2) Photo Defined Electroforming: the Thick Resist Method

With Photo Defined Electroforming, a thick pattern of photoresist is used during photo defined growth, such that the thickness of the product (T) does not exceed the thickness of the photoresist (TR).

Aspect ratios (TR/ WR) up to 1 can generally be achieved with ease. The exact limits depend on the size and geometry of the products .

(3) Surface replication with Electroforming

With surface replication, positional accuracy is determined by stress in EF material and accuracy of exposure method (For glass tooling and LDI the accuracy is so high that the accuracy in the final product is solely determined by the EF process).
surface replication with ElectroformingGenerally, positional accuracy of the LDI/glass tooling is ±0.15‰ and film tooling ±0.25‰.

Feature accuracy of overgrowth is ±2 µm and ±0.75 µm on standard deviation on a 50 µm thick product.
Accuracy of features on photo-defined is generally ±5 µm for LDI/glass tooling and ±10µm for film tooling.
For mm/cm size features, the accuracy drops by ±0.15‰/±0.25‰.

3. Why choose Electroforming over other technologies?

Electroforming vs 3D printing

Electroforming and 3D Printing are both additive manufacturing processes. Whereas Electroforming builds up precision metal parts atom by atom, 3D Printing works by applying materials in droplets through a small diameter nozzle and “print” layer by layer to build up the product. 

(1) Cost Efficiency

A 3D printer and its corresponding materials can be cheaper than electroforming equipment, so 3D Printing seems more cost-effective when you want to create just a small amount of products yourself in-house. When you are going for industrial scale production, however, the higher the volume, the more favorable Electroforming becomes.

(2) Lead Time

3D Printing of metal parts is still in its infancy. The technique entails printing with minuscule metal powdered parts. After printing, the metal needs to be heated (sintered) in order to suture. In addition to the time-consuming sintering process, the printed layers also need to dry so that they don’t sag. These two steps both take a considerable amount of time, which makes 3D Printing a relatively slow procedure for fabricating metal parts. Additionally, 3D Printing can only deal with one part a time. Electroforming, on the other hand, is much faster a process, during which you can grow a large number of parts simultaneously (in one electrolytic bath).

(3) Design Complexity

Electroforming allows for great design flexibility as it requires almost no tooling investment and that it has a very short lead time. With regard to material, however, Electroforming mainly works with nickel and copper. For medical applications, for instance, nickel components can be coated with a layer of a PdNi alloy. 3D Printing also allows for high level of design flexibility and range of material usage are much wider.

(4) Quality/Accuracy

Electroforming allows you to grow material on a micro scale, resulting in absolute accuracy and high aspect ratios. The standard deviation of electroformed parts is less than 1% of the material’s thickness. Orifices of just a couple of microns are no exception. 3D Printing can currently achieve 100 micron range of precision at its best. The technique can be 100 times less precise than electroforming.

Compared to 3D Printing, Electroforming has higher accuracy, shorter lead time, and better cost efficiency especially when it’s large volume. 3D Printing allows for better design flexibility mainly due to the fact that it works with a wider range of materials.

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Electroforming vs Chemical Etching

Chemical Etching is a subtractive manufacturing process applied in microfabrication of precision metal parts. Similar to Electroforming, it is known as a fast, accurate, and cost effective manufacturing method to deliver high precision, burr- and stress-free precision metal parts.

(1) Cost Efficiency

The most common rule of thumb is the higher precision it is, the more expensive it gets. Electroforming is an ultra-precision manufacturing technique, allowing for higher accuracy and tighter tolerances than Chemical Etching. Thus it is commonly assumed that Electroforming is a more expensive process than Chemical Etching. While in some cases that is true, in some others, it is not. Depending on product design and specifications, Electroforming can also be more cost-efficient than Chemical Etching. With electroforming in high volumes the mandrels can be used several times. Sometimes even up to 20 times. Making the EF process very cost effective.

(2) Lead Time

Electroforming is a precision manufacturing process that can harvest a large number of products in every run, which makes it more time-efficient than most other precision fabrication techniques. Chemical Etching goes through a similar process to that of Electroforming and thus also has a short lead time.

(3) Design Complexity

When it comes to the feature specification, the Chemical Etching process doesn’t allow for control of the hole geometry like Electroforming does. With Electroforming, the unique shape resulting from the overgrowth method cannot be realized with Chemical Etching. However Electroforming comes with the limitation on material: mainly nickel and copper can be electroformed, while virtually all metals can be chemically etched with no restriction in hardness of the material.

(4) Quality/Accuracy

With Chemical Etching, a high level of accuracy and precision can be achieved. Electroforming allows you to grow material on a micro scale, providing absolute accuracy and high aspect ratios. The standard deviation of electroformed parts is less than 1% of the material’s thickness. Thus compared with Chemical Etching, Electroforming is at an even higher level of precision.

Electroforming is a precision manufacturing process with higher accuracy and shorter/similar lead time compared with Chemical Etching. It allows for better design flexibility when it is about hole geometry; when it is about material choice, Chemical Etching has the advantage. Electroforming can be more cost efficient than Chemical Etching, depending on product specifications.

Electroforming vs Laser Cutting

Laser Cutting is a subtractive manufacturing process. It works by directing the output of a high-power laser most commonly through optics to cut materials in order to achieve the desired products. Compared to Laser Cutting, Electroforming is the more optimal choice when it is large volume production of precision thin metal parts, especially when the design is complex and quality/accuracy demand is high. 

(1) Cost Efficiency

When it’s a small volume production or prototyping, Laser Cutting can be more cost-effective than Electroforming. When it’s industrial mass production, however, Laser Cutting loses its advantage in costs and Electroforming becomes the favorable option.

(2) Lead Time

With Laser Cutting, you can’t produce multiple parts simultaneously, while with Electroforming you can. Compared to Laser Cutting, which can only deal with one component after another, Electroforming is a process that can harvest a large amount of products in every run. When production volume is very low, Laser Cutting might have an advantage in speed over Electroforming. However, when it is industrial production, lead time of Electroforming is shorter.

(3) Design Complexity

Electroforming and Laser Cutting are both highly flexible regarding design. When the design is very complex, however, Laser Cutting might take much longer time since it can only deal with one part/feature after another while Electroforming works on the complete design simultaneously and can harvest a large amount of product in one run. When it comes to materials, Electroforming has some limitations while Laser Cutting can work with a wider range of materials (learn more about what materials can be electroformed from a previous blog).

(4) Quality/Accuracy

Electroforming is a high precision manufacturing process that does not change the properties of metals such as hardness, grain structure, or ductility. With Electroforming, you can harvest ultra-precision thin metal parts burr- and stress free. Laser Cutting, on the other hand, is a thermal process which results in thermal stress, as well as micro burrs.

Thus, compared to Laser Cutting, Electroforming is the more optimal choice when it is large volume production of precision thin metal parts, especially when the design is complex and quality/accuracy demand is high. When it is about material choice, Laser Cutting has the advantage over Electroforming.

Electroforming vs Stamping

Stamping, also known as pressing, is a manufacturing process that place flat sheet metal into a stamping press, where a tool and die surface forms the metal into the desired shape. The trend of miniaturization has driven the industry to the micro level, which is referred to as Micro Stamping. Compared to Stamping, or Micro Stamping, Electroforming has shorter lead time, lower costs, better quality, and more design flexibility.

(1) Cost Efficiency

Unlike Electroforming which has no tooling cost, Stamping always requires substantial investment in tooling and installation: both monetary wise and time-wise. One stamping die can easily cost thousands of dollars, not to mention the extra costs for setting up and maintenance costs over time.

(2) Lead Time

With Stamping, the lead time can be 6-8 weeks only for preparing the tooling. Even after the stamping tool is completed, extra time (and costs) will incur for setting up the tooling in the stamping press. With Electroforming, lead time is a matter of days. Compared to those who still stamp their precision metal components, you can receive your ultra-precision electroformed parts even before their stamping tool is ready! 

(3) Design Complexity

Electroforming allows for more design flexibility as it requires no hard tooling and that it has a very short lead time, while with Stamping modifying a design means making a completely new die and investing on tooling and setting up all over again. This also means that Electroforming is perfect for small amount prototyping as well as industrial production. When it comes to material choice, however, Stamping allows for more flexibility than Electroforming.

(4) Quality/Accuracy

Electroforming is an ultra-precision micro-manufacturing technology. With Electroforming, a higher level of accuracy and precision can be achieved. Moreover, electroformed parts are completely burr- and stress-free while stamped parts feature partial burrs and stress at cutting edge. Although minor burr or stress can be acceptable for some applications, it might be a stumbling block for your next breakthrough.

Thus, compared to Stamping, or Micro Stamping, Electroforming has shorter lead time, lower costs, better quality, and more design flexibility (when the material is not an issue).

4. What can be achieved with Electroforming?

features enabled by Electroforming

(1) Parts with micro holes

Electroforming is an Additive Manufacturing process particularly suitable to create accurately defined holes, from single hole products to meshes of millions of holes for atomization.

Veco has two major technologies to offer, leading to different hole shapes: bell mouth (tapered) and cylindrical (straight) hole shape.

Features

  • Miniaturized holes down to 2 micron
  • Ultra-precise hole geometry
  • Well-controlled pitch accuracy
  • Ultra-smooth surface free of burrs or blocks

(2) Precision optical parts

Ultrafine detail and tight tolerances achievable with Veco’s precision technologies are perfectly suited to the optical industry, where absolute accuracy is critical to the majority of applications. We manufacture customized, highly accurate optical parts for a wide variety of micro-optical applications.

Features

  • Excellent edge definition and roundness
  • Various plating finishes possible
  • Exceptional shape accuracy and consistency
  • Customized design and development

(3) High precision metal parts

With the world-leading precision solutions in house, there are endless possibilities for high precision metal parts: nozzles, slits, any freeform geometries, and complex patterns. If you can imagine it, we can make it.

Features

  • The Additive Manufacturing process (atom by atom)
  • Fracture free surface
  • Completely smooth edges
  • Low bend radius down to 0.04mm
  • High aspect ratio

multi-layer Electroforming: more than just 2D

Electroforming is known as a high precision manufacturing process for 2 dimensional thin metal parts, but that’s not the full picture. Nowadays with the trend of miniaturization components are becoming smaller and more complex. Some high precision metal parts demand not only extreme accuracy but also delicate structure in all dimensions. This is when multi-layer electroforming comes into play.

Electroforming is not limited to producing 2D structures because additional layers can be grown by repeating the deposition process. These additional layers can reinforce thinner electroformed parts, making them less fragile thus easier to handle. Moreover, the fact that additional layers can be grown in different directions means unique delicate structures can be made to meet complex design demand.

The multiple layer capability brings new possibilities for many industries that demand complex precision metal solutions. Inkjet nozzle plate is one example. In this case, the nozzle plate was electroformed using the overgrowth method (plating defined), and subsequently the ink chamber was electroformed using the thick resist method (photo defined), resulting in high performance digital printing.

altering material properties with Electroforming

Electroforming allows for alteration of material properties, so different material properties can be achieved with the same material. Such alteration can be achieved by manipulating the crystal structure of the material. By changing the deposition conditions, amorphous nickel deposits can be made; such nanocrystalline material is usually very smooth and hardly ferromagnetic. Thus by controlling the material’s structure, the component’s magnetic properties become almost non-existent, so non-magnetic components can be made of a material that usually has magnetic properties.

Besides magnetism, material hardness can also be controlled with Electroforming by manipulating its crystal structure. A material that contains crystals of only a few nanometers in size will turn out hard. As the size of the crystals increase, so will the softness of the material.

When altering material properties doesn’t suffice, for example if high corrosive resistance is demanded for special application, or a particular material is necessary to be in contact of human skin, that’s when coatings comes in. A layer of material such as palladium or gold can be coated followed by Electroforming process.

5. Case studies: innovations enabled by Electroforming

Electroforming: empowering the next-gen PV cell manufacturing

The demand for energy transition is constantly increasing, especially since the Paris Agreement stipulates that the world must become greenhouse gas neutral by the second half of the century to limit the increase of global temperatures to a maximum of 2°C. Solar power plays a very important role in energy transition and climate protection as it affords a drastic reduction in greenhouse gasses, which arise through the burning of fossil-based fuels such as oils, coal and gas.

In this context, accumulated research and effort has been taken to improve the efficiency of solar power. Crystalline silicon (Si) photovoltaic (PV) cells are the most common solar cells used in commercially available solar panels. They have dominated the PV cell market since its early beginnings, around the 1950s, and account for more than 90 percent of it today.

The outlook for higher efficiency in photovoltaic cell manufacturing — from better screens to no screens

A large number of PV cell manufacturing companies and research institutes have been devoted to improving cell efficiency and reducing costs to develop high-efficiency crystalline Si PV cells. An essential step in producing these cells is the metallisation process of creating a grid of very fine lines on the front side of the wafer that conduct the light-generated electrons away from the cell.

This metallisation process is most often undertaken using screen printing technology, whereby conductive paste is forced through the openings of a wire mesh or emulsion screen onto the wafer to form the circuits or contacts. Over the years, efforts to improve the efficiency and precision of PV cell metallisation have led to better screen printing equipment and materials. For example, high-precision stencils have been introduced as an alternative to traditional wire mesh and emulsion screens. Moreover, the development of inkjet printing and 3D metal printing technologies has allowed for the realisation of maskless screen printing.

(1) Screen printing

The screen printing process begins with an Si wafer being placed on a printing table. A screen, usually a wire mesh or emulsion screen, is mounted within a frame and placed over the wafer. This screen blocks certain areas and leaves other areas open. Metal paste, usually silver (Ag), is then dispensed onto the screen using a squeegee so that it is spread uniformly to fill the screen openings. As the squeegee moves across the screen, it pushes the paste through the openings, transferring it onto the wafer.

A grid of conductive circuit lines is deposited this way. These thin and delicate lines, also referred to as fingers, collect and conduct the light-generated electricity from the active regions to larger collecting lines, or busbars, and then to the module’s electrical system.

However, the lines are not as thin as desired, since they block sunlight from reaching active parts of the cell and thus reduce conversion efficiency. To minimise this so-called shadowing effect, efforts have been made to make the lines as narrow as possible as well as taller to maintain the same cross-section for adequate conductivity. 

screen printing process

screen printing process illustration

(2) Stencil printing

The stencil printing process was introduced after the screen printing process. The development of high-precision metal manufacturing technologies such as electroforming meant that high-precision stencils became an alternative for achieving achieve finer, taller contacts in PV cell manufacturing. As in screen printing, these stencils, with blocked and open areas, are used to apply paste to the wafer.

Stencil printing overcomes the limitations of screen printing in aspect ratio (i.e. line height/line width), finger width and uniformity. The much finer lines with higher aspect ratio and better durability. All of these in the end lead to much higher yield and lower cost. Lab tests have shown stencil printing as offering a 0.25 percent PV cell efficiency improvement over screen printing. 

Electroformed Solar Cell Stencil

Electroformed Solar Cell Stencil

(3) Inkjet printing

Inkjet printing is an extremely versatile, non-contact process that involves jetting tiny ink droplets to facilitate direct printing. Besides printing graphics on all kinds of surfaces, industrial inkjet printers today can deposit a wide range of inks with ultra-precise accuracy on various substrates. Thanks to inkjet printing being non-contact and that available inks range from polymers and metal nanoparticles to living cells, inkjet printing has seen a surge of new applications in fields including electronics, life science, PVs and optics.

In PV cell manufacturing, inkjet printing deposits metal paste directly onto the surface of the cell through very miniscule openings of a highly efficient, parallel print head, providing a contactless, maskless printing alternative to conventional screen printing and stencil printing. This dispensing process provides the PV industry with multifaceted benefits over conventional screen printing, such as those outlined below.

Increased efficiency and electricity output

In screen printing, a squeegee is used to push the metal paste through the screen openings and onto the wafer surface. The typical line width is 55–80 μm, resulting in shadowing loss of 7–10 percent. Moreover, lines have a low aspect ratio of c.a. 0.2–0.5.

In inkjet printing, the lines can be made much thinner, exposing a larger semiconductor surface to the sunlight. The lines also have a better aspect ratio, ensuring a larger portion of incoming sunlight is reflected towards the wafer instead of back into the air. These two factors increase efficiency by approximately 1 percent and electricity output.

Reduced metal paste consumption

In screen printing, the wire mesh and emulsion screens are repeatedly used and the openings can gradually get blocked or deform, resulting in lines broadening, becoming irregular and having ragged edges.

In inkjet printing, finer lines with higher aspect ratios and lower striations can be achieved. Moreover, high-speed dispensing using intermittent parallel operation of hundreds of nozzles down to several micron can be flexibly optimised in terms of nozzle number and arrangement. The accuracy and flexibility enable homogeneous line shape, contributing to a 20 percent reduction in metal paste consumption.

Significant throughput potential

Inkjet printing, being non-contact, promises a lower reject rate if used on thinner Si wafers. Also, being inline, it increases throughput significantly over conventional screen printing.

To sum up, the maskless nature of inkjet printing affords a high material utilisation rate, improved output and efficiency, freedom of design and significant throughput potential. Moreover, it can be directly integrated into an existing silicon PV cell production facility, replacing the screen printing process utilised for front-side metal contacts.

How electroforming has empowered the contactless metallisation process

A vital part of the dispensing print head is the high-precision nozzle plate, produced using electroforming, a micro-precision, metal additive manufacturing (AM) process combining lithography and electrodeposition. The nozzle plate is a rectangular, elongated part with miniature holes, through which the metal paste is pressed and deposited via the nozzles onto the PV cell in very thin straight lines.           

inkjet nozzle plates

inkjet nozzle plates gold plated

Another significant advantage of  electroforming is reproducibility. The process affords precision of approximately 5 μm. In a plate that has 100 to 200 miniature nozzles in a straight line, each of those nozzles needs to be the correct size, not only on each plate but on every plate and across different batches of the plate. Electroforming guarantees reproducibility, meaning the same drawing and process setup translates to perfectly uniform and reproducible printing results and the exact same product time and time again.

Electroforming can also be used to produce special hole geometries; for example, bell mouth shaped holes not achievable using traditional cutting and drilling processes. These holes can effectively reduce blinding/clogging of the plate/nozzles, thus ensuring exceptional paste release performance.

A final point of note is that plate material resistance is especially important in PV cell production because the metal paste used can be corrosive. Also, the pressure applied to push the paste through the plate makes deformation a potential risk. For these reasons, Veco offers a range of alloys that have highly stable contact resistance and excellent mechanical characteristics, ensuring exceptional printing performance over a longer lifetime.

Electroforming: the future-proof solution for miniaturized contacts

Semiconductor companies are faced by constant pressure to outperform their competitors and deliver the next ‘big thing’ – to produce parts that are smaller, more durable, and more powerful, all while maintaining cost efficiency and sustainable production. In an industry characterised by rapid technological evolution and constant innovation, this is a full-time task. To this end, it’s essential that semiconductor manufacturers are able to prototype new products with extreme efficiency.

We’ve been working with Multitest since 2010, and helped them along the way of being international leader in semiconductor manufacturing. In this blog, we’ll take a look back at our project with Multitest and the work we’ve done with them over the years. Specifically, we’ll look at the operational and financial benefits that our Heat Resistant (HR) nickel provided them in both their testing and production processes.

About Multitest

Over the past decades, Multitest has grown from a start-up company into one of the world’s leading manufacturers of testing equipment for semiconductor Integrated Circuits (ICs). In that time, they’ve gone from a company of four members and a handful of local clients, to a multinational corporation with hundreds of employees, serving a growing number of international partners. Multitest has offices in over 20 locations across Europe, Asia, and the USA, and is a trusted partner to the world’s most renowned semiconductor manufacturers.

Multitest provides innovative test handling and test interface solutions, tailored to suit the individual requirements of each customer they partner with. They pride themselves on delivering high throughput rates, micron-scale measurement, precision temperature accuracy, and the latest technology for measurement and production.

Before Veco: The challenges faced by Multitest

When Multitest approached us with the challenge of improving testing efficiency and profitability, they were looking for an electroforming partner who was not only able to deliver samples of the highest possible quality and reliability but also to do so at an industrial scale.

Veco’s ability to produce large volumes of parts rapidly and at scale made us a perfect fit for them. Our relationship with Multitest started in 2010, when we began supplying them with electroplated micro-precision parts.

When Multitest took us on as a supplier, they started growing at a rapid rate, and looking for ways to increase efficiency and adapt to the new scale that their increased demand required. In order to achieve their goals, we would need to develop an innovative and unprecedented strategy. To this end, we started working on a new project together, using what we’ve subsequently come to call our experimental approach to prototyping ( read more about the approach to co-developing with us here) and our newly-developed HR nickel technology.

How Veco’s Electroforming technology helped Multitest as a global leader in semiconductor ICs

Multitest’s high production demands and their exacting quality standards means their testing process was intensive, and required a high degree of accuracy, reliability and stability. The semiconductor parts produced by Multitest are extremely small – often only a few hundred microns in height.

Testing with high precision probes has some principal challenges: the probes are subject to rises in temperature during the testing process, which can cause instability and even failure if the material is unable to handle it. Because of Multitest’s stringent quality requirements, they needed their probes to be constructed from a metal that is durable enough to handle the stresses involved in their testing process without it changing properties.

Heat Resistant (HR) Nickel is a unique form of nickel developed by Veco to withstand the stresses involved in the rigorous testing methods used by semiconductor producers. It’s based on entirely different additives to the nickel products developed by our competitors, and has a high heat resistance and conductivity. This makes it possible to subject components to extensive and intensive testing without the material changing properties, and ultimately makes the testing process more consistent and reliable.

How Veco and Multitest’s partnership resulted in increased efficiency and profitability

  1. HR Nickel makes testing more reliable and profitable

    Using our HR Nickel hasn’t just improved the reliability of Multitest’s testing process: it allowed them to increase the profitability and productivity of their entire business. By using a metal that is better suited to the stresses of semiconductor testing, failure rates are significantly lower, and getting accurate testing results is faster, more reliable and more affordable, without compromising on quality. A principal challenge that Multitest had with other suppliers was that their testing probes were suitable for testing, but weren’t resilient enough to be used in millions of measurement cycles. HR nickel makes it possible for Multitest to run several million tests on their components before they show any signs of wear (Up to three times more than conventional components), and are suitable for both testing and production purposes.

  2. Electroforming gives you access to high-precision parts at scale

    Electroforming differs from other techniques in that it allows manufacturers to ‘grow’ parts atom by atom, which provides accurate, high aspect ratios. Electroforming is an Additive Manufacturing technology. Unparalelled high accuracy is achived by a Lithographic process combined with this Electroforming process.

    Electroformed components have an extremely clean and smooth surface quality which is burr and stress-free, with straight side walls, sharp edges and accurate hole sizes impossible to achieve through other techniques. It also allows for exceptionally short lead times both in prototyping and production. In practice, this allows Multitest to achieve near-perfect process control, high repeatability and top-quality component production – in other words, it’s the perfect solution for manufacturers looking to achieve high production volumes at minimal cost.

  3. A shared vision and co-development helps us achieve and exceed Multitest’s goals

    We’ve helped Multitest achieve many operational benefits during our time working with them, but I believe it’s the way we approach our partnership that adds the most significant value to them: instead of a traditional supplier/manufacturer relationship, Multitest and Veco work hand-in-hand with Multitest every step of the way, which ensures our visions are aligned at all points. On the technical side, our Application Engineers co-operate with Multitest’s engineers to develop solutions co-operatively. Our relationship with their engineers is ongoing, and we have regular check-ins to ensure we’re consistently helping them achieve their targets. We also share a KanBan system with their purchasing department, which allows us to keep their main parts on stock for fast delivery.

    The fact that we work so closely alongside Multitest’s engineers and purchasing team also means that we have a unique insight into the context of their business, the challenges they face and the goals they hope to achieve. This means we’re able to provide them with a tailored, innovative solution that is based on their specific demands and requirements.

What makes Electroforming the future-proof solution for miniaturized contacts

  • Higher precision sub-micron tolerated versatile tubes

    The electroforming process is very flexible: your design can be changed easily without the need for expensive tooling costs. By its ability to produce very fine curved shapes it surpasses conventional technologies like stamping and punching. Radii as small as 30 microns can be made in relatively thick (30-100 micron) material.

  • Higher density and further miniaturization of intercircuits

    With electroforming, it is possible to keep up with the demands for HD intercircuits. It is possible to make very slim designs with high aspect ratios. This means that very small products can be made without compromising on reliability. Aspect ratios achieved with electroforming are up to 3 times higher than with conventional stamping or punching.

  • Smoother surface for enhanced reliability

    The contact surface is free from burrs, fractures, or stress, which leads to enhanced reliability of the contact products. Also, a combination of materials — as well as surface finishing — is possible to increase the functionality of the product.

  • Better material developed dedicated for increased contact

    Special Electroformed materials have been developed to maximize the functionality of the products. Materials up to 600 Vickers hardness with a very high thermal and electrical conductivity exist. The “spring” behavior of these materials results in a very long lasting product without wear.

6. Video playlists of Electroforming

Knol-edge: What does Knol say about Electroforming

Technology videos

Quiz: test your knowledge about Electroforming?

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