A New Soldermask for Eurocircuits’ PCBs.

Last year we made one of the group’s largest investments by installing the Ledia direct imaging system in our plant in Eger – Hungary. We can use Ledia to expose inner layers, outer layers and Soldermask as well. With the Ledia we can produce PCB’s with tighter tolerances on images and Soldermask.

To better optimize all advantages that Direct Imaging of thev Soldermask with the Ledia has to offer, we needed to change the Soldermask to another type. Still from the same supplier, Sun Chemicals, CAWS2708 LDI is better suited for the Ledia’s imaging process.

With this new, professional and reliable Soldermask, we can expose our production panels faster than with the previous type. In combination with Direct Imaging, we can also achieve much better results on registration accuracy.

The surface of the new Soldermask is perfect for soldering. The matt finish helps with the alignment for placing components and it is better suited for automatic optical inspection after soldering. We are convinced that this Soldermask is a modern and user-friendly product.

  

We made lot’s of tests with the new Soldermask and all test results were very convincing. The many micro sections we have made, show that the thickness and coverage of the Soldermask are also very good. We measured at least 10 micron of Soldermask on the edges of the tracks.

The left picture shows the Soldermask we use in Eurocircuits Eger and the right picture shows the Soldermask of Eurocircuits Aachen.

 

In Eurocircuits Aachen we are using the sister product of the CAWS2708 LDI of Sun Chemical. The CAWN2295 used in Aachen has the same RAL colour of the one in Eger and has the same technical features. Nevertheless, there will be optical differences between the two because of the different application method. We use curtain coating in Germany and spray coating in Hungary.

The physical and chemical properties of both Soldermask types are the same after the curing process and both have very good electrical properties. Last but not least we can state that the new Soldermask has excellent characteristics for the adhesion to the copper surface.

To summarize we can conclude that the new Soldermask types we use in Eger and Aachen have better characteristics than what our customers were used to before although they might look a bit different than the previous types.

Eurocircuits Technical Update – direct imaging technology

In this update

  • New direct imaging technology – more capacity, more design options
  • 2015 – a record start to the year
  • Medium-volume BINDI pool now UL approved – and 4 layers soon
  • Eurocircuits sponsor student projects

Direct-imaging technology

MORE CAPACITY

The Ledia V5 direct-imaging system, installed in January, is our largest single investment in a single piece of equipment – and is already paying off. Direct imaging has boosted our production capacity in time to handle the fastest growth in orders we have seen in years. See how it works in our technical BLOG.

MORE DESIGN OPTIONS

The reliable assembly of new-generation BGAs, QFNs and fine-pitch leaded components demands tighter-toleranced soldermasks. Ledia images finer soldermask dams than conventional phototools. We will use it in conjunction with our forthcoming solder-bridge pre-CAM tool to produce the optimum soldermask solution for your designs.

2015 – a record first quarter

Q1-2015 we served more than 5,500 customers with almost 24,000 orders. Thus we are up 15.8% and 18.5% on the first quarter of 2014. And 2014 was already a record year.

BINDI pool news

  • Our BINDI pool service for orders up to 50 m2 is now UL approved. UL marking can be added to your boards at no extra cost
  • From May BINDI pool will offer 4-layer multilayers as well as 2-layer PCBs

Student project sponsorship

We have sponsored student projects across Europe for many years as part of our commitment to foster new generations of electronics designers. See our BLOGS for some recent projects. If you are looking for sponsorship for a student or educational project, contact us at euro@eurocircuits.com.

Technical blogs

Some recent highlights, all now available in English, French. Spanish and Portuguese:

If you would like us to produce a blog or white paper on a particular aspect of PCB manufacturing technology, PCB soldering or EAGLE CAD, email us at euro@eurocircuits.com.

Meet us

The best way to share ideas and knowledge is face to face. Come and meet us at:

How Often Can You Raise a Eurocircuits PCB to Lead-free Soldering Temperatures?

Gold plating for edge connectors

Gold Plating over Edge Connectors

Eurocircuits offer two types of gold finish: Electroless Nickel Immersion Gold (ENIG) as a surface finish for the whole PCB, and hard plated gold over plated nickel for edge-connector fingers. Electroless gold gives excellent solderability, but the chemical deposition process means that it is too soft and too thin to withstand repeated abrasion. Electroplated gold is thicker and harder making it ideal for edge-connector contacts for PCBs which will be repeatedly plugged in and removed.


Technology

We plate the hard gold onto the PCBs after the soldermask process and before we apply the surface finish to the rest of the board. Hard-gold plating is compatible with all the other surface finishes we offer.

We first plate 3 – 6 microns of nickel onto the edge connector fingers and then on top of that 1 – 2 microns of hard gold. The plated gold is not 100% pure; it contains some cobalt to increase the wear-resistance of the surface.

We normally bevel the edge connectors to ensure easy insertion. Bevelling can be specified in the order details.

To make sure that the gold fingers align exactly with the edge-connector profile, we rout the vertical edges of the connector on the first drill run. The edges of the connector are then exactly aligned to the printed image.

In some cases one or more gold fingers are shorter than the rest, so that the longer pads connect first when the PCB inserted into the connector. This means that the shorter pads cannot be connected vertically to the plating bar. They have to make the connection needed for electroplating in another direction (see illustration. Here the blue lines represent the profile added at first drill stage and the green the final profiling).

After plating we check the adhesion of the plated nickel and gold with an industry-standard tape-test. We measure the thickness of the plated layers with a non-destructive X-ray measuring machine.

Limitations of the technology

  • The plated pads have to be on the edge of the PCB, as this is an electroplating process. There has to be an electrical connection between the plated pads and the production panel frame.
  • The maximum length of the plated pads is 40 mm as we use a standard shallow plating bath .
  • Inner layers have to be free of copper at the edge of PCB. Otherwise the bevelling could expose the copper.
  • If you want your PCBs delivered in a customer panel, the panel frame/border must be open on the edge connector side to allow us to make the connection for electroplating.
  • We can plate hard gold on two sides of PCB. But if the connectors are on the opposite sides of the PCB there has to be a minimum 150 mm between them.
  • To ensure optimum quality surface-finish, do not place any plated holes (PTH), SMD or other pads closer than 2.00 mm (80 mil) to the gold fingers – see drawing.

Soldermask on via-holes in case of chemical Nickel-Gold surface finish

Soldermask on via holes

Updated 03 July 2020 – Via Filling with Soldermask discontinued and replaced by Via Filling with Resin providing a overall better solution.
There are 3 ways our customers prepare their layouts with respect to covering via-holes with soldermask:

  • Vias open (not covered by soldermask) on both sides of the PCB
  • Vias closed (covered with soldermask) on both sides of the PCB
  • Vias open from one side and covered from the other side of the PCB

As necessary background information we need to briefly introduce you into the technology of applying soldermask to the boards.


  • First we cover the whole surface of the production panel with soldermask ink and then dry the panel (printing the soldermask)
  • The ink we use is a UV sensitive material. When exposed to UV-light, the ink will harden (exposing the soldermask)
  • Ink that is not exposed remains soft and can be washed away using a 1% alkalic solution (developing the soldermask)

The easiest production method is to have all vias open from both sides. The vias will be clean. They will not contain any contamination nor soldermask. The next picture shows vias free of soldermask. We did not expose the soldermask on the via pads so that it remains soft and is washed away during the developing process.

Another practical production method is where the vias are covered on both sides of the PCB. We expose the soldermask on both sides of the via-pad and via-hole so it will harden and sthttp://www.eurocircuits.com/images/stories/Movies/02_set_the_stencil_on_the_frame.flvay on the via-pad and over the via-hole to close it. There is a risk however that (mostly in case of via-holes with a larger diameter) the via-hole is not completely covered and a small opening remains in the middle.

There is a danger that chemicals get stuck in these small openings during the processes that follow after the soldermask application. These chemical can contaminate and affect for instance the chemical Ni/Au process. A further danger exists that chemicals of the Ni/Au process remain in these openings and as they are agressive chemicals they might keep on reacting in the via hole years after the board has been produced causing possible failures in usage of the PCB in its application.

The third case (vias covered from one side and open from the other side of the PCB) is the most problematic in production. This design creates a pocket. We expose the soldermask from one side but not from the other side. This soldermask in the middle of the via-hole will only be half polymerised. During the baking process this material can come out of the hole from the open side and contaminate the copper surface and thus disturb the surface finishing process. The pictures below shows a typical failure.

Vias and Chemical Nickel-Gold (ENIG)

Vias that are not completely covered or not properly filled with soldermask may create “skip pads” in the ENIG process.

Till now we didn”t receive any reasonable explanation from our material suppliers nor did we found one elsewhere that reveals the source of this problem. However supplier advise and long term experience guide us to two possible solutions to avoid the issue:

  • Modify the layout so that all vias are open. Our engineers favour this solution. Sadly this is not always accepted by our customers or the design may not allow it.
  • Apply the soldermask after the ENIG process. This is a costly solution as all copper surfaces are gold-plated and the soldermask adhesion becomes worse.

 

Updated 03 July 2020 – Via Filling with Soldermask discontinued due to Via Filling with Resin providing a overall better solution.

For closed via-holes we have developed an alternative solution which avoids chemicals getting trapped in the partially closed via-holes during developing of the soldermask or during application of the Ni/Au. Before the coating the entire panel with soldermask we selectively print soldermask into the via holes using a stencil. During a second print run we then cover the whole panel. This way the via-holes are completely filled with soldermask. An even layer of soldermask now covers the via-holes leaving no pockets to hold residual chemicals. We have used this technique for over 6 months, and it has proved successful in dramatically reducing the number of skip pad problems.

The following movies show this process of via filling and soldermask printing.

Setting up the machine:

Printing the soldermask into the via holes:

Result after filling the via holes:

 

Cover the panel with soldermask

Result after printing the soldermask

Drying the soldermask layer: