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At my place of work, we use soldermask colors as a sort of poke-yoke for manufacturing purposes E.g. Technicians know that green pcb goes with green, blue pcb with blue, etc. This has lead to some ... esoteric color choices including matte white, hot pink, blue/red sunburst, etc. for our soldermask. Our board fabs are usually happy to oblige, and we have had no reason thus far to question the dye choices.

However, during a discussion with a manufacturer about quality defects, their production engineer claimed that dye's used to make the soldermask color have a subtle impact on reflow, creepage, solderability, electrical conformance and dielectric effect. Specifically citing increased risk of soldermask voids and solder spreading under the soldermask layer for blue dye solder masks.

Is there any validity to this, or research to support this claim?. Moreover, are there any differences that could conceivable have an effect. For example, reflow temperature considerations when using very different solder mask colors (e.g. gloss white vs matte black) but nearly identical PCB and components.

I assume any material differences are up to the PCB material supplier, and while I am sure in that domain there are different materials and dye's used, I have always assumed it to be equivalent if it is offered as an option by the fab.

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    \$\begingroup\$ It depends, is this for a audiophool product? If so, color can make a huge difference to the final sound. The less measurable and repeatable the effect is, the more you can charge for it. \$\endgroup\$ – Olin Lathrop Jul 31 '18 at 22:11
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    \$\begingroup\$ @OlinLathrop haha, but no, its an industrial product with very high requirements for process control. This was brought up as a possible defect source in the context of QA. It sounded like BS to me at first, but like Tin whiskers is one of those corner case things that might conceivably be real in the right situation and set of conditions. I guess this question is more about the dye chemistry used to mix this stuff \$\endgroup\$ – crasic Jul 31 '18 at 22:13
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    \$\begingroup\$ Anecdotally, green soldermask can have better resolution than black, according to the maker of the Teensy dev board: forum.pjrc.com/threads/24950-Teensy-3-1-Changes-To-Green-PCB \$\endgroup\$ – Abe Karplus Jul 31 '18 at 22:15
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    \$\begingroup\$ I would listen to the opinion of production engineer from PCB manufacturer, they likely have a lot of experience. However, my feeling is that the dye color is a minor constituent of the coating material, so the electrical differences should be minuscule. However IR solder reflow should be really affected by the mask color, most differences I would expect between shiny white and matte black. \$\endgroup\$ – Ale..chenski Jul 31 '18 at 23:35
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I'm certainly no expert, but the other day I came across this article from a PCB manufacturer that I would like to bring to your attention. It states:

  1. Green solder mask is physically superior

Due to the traditional aspect of using green pigments, R&D into making better solder mask oils focused on the standard green color. The actual chemical pigments used influence the performance of the resin during application and in the field. When demand is pushing form factors to their limits, no one cares about having pink boards. As a result, green solder mask now has superior properties compared to other aesthetically orientated colors.

Most prominently, commercial green solder mask is the only available color that can reliably produce solder mask dams of 0.1mm (4mil). Next up is red, yellow and blue that can produce 0.12mm dams and then black and white which can only achieve 0.15mm. Solder mask dams are vital for ICs and fine pitch components since they are valuable in preventing solder bridges from forming.

enter image description here

So yes, based upon this information I would say that there are differences in quality, as the factory itself states. Green would be the way to go for best quality.

Hope this helps.

Edit: Added picture of solder mask dam, from here

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  • \$\begingroup\$ This is a good point, and well taken. However, presumably would be brought up during TQ if the tolerances requested were beyond capabilities. In other words, these are valid concerns that should be handled appropriately by the production specialists. The approach I have taken is to inquire with pcba production, how they take board color into consideration during processing. \$\endgroup\$ – crasic Aug 2 '18 at 3:32
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    \$\begingroup\$ As an aside, worthy of its own question and answer, soldermask damming between small pitch pads to prevent bridging is not generally worth doing regardless, in production pcba (not hand assembly) this is handled by shrinking the aperture on the stencil to be smaller than the pad (Paste layer in footprint) limiting the amount of solder paste and eliminate smearing, once this is dialed in the likelihood of bridging should be very low. \$\endgroup\$ – crasic Aug 2 '18 at 3:33

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