Solder Mask Discoloration on PCBs

Guide to Solder Mask Discoloration

Careful inspection of your printed circuit boards (PCB) may be second nature in your industry, and the first time you saw solder mask discoloration on a circuit board, you may well have been alarmed.

Whether you observed white patches on a PCB, dark stripe PCB solder mask discoloration or some other type of solder mask discoloration, it’s natural to immediately want to know if the PCB is still good, if the discoloration will cause some kind of problem, what caused it and how to prevent it from happening again. Here is a quick guide to solder mask discoloration.


Dangers of Solder Mask Discoloration on a Circuit Board

The reality is that in most cases, any kind of PCB solder mask discoloration is probably cosmetic and does not represent any damage to the board that will affect its functioning. However, it is possible that whatever caused the discoloration defect may in itself be a faulty component or process that could cause problems to the board independent of the discoloration, so it’s a good idea to identify just why the solder mask discoloration is happening.

While it may be difficult to isolate the exact cause on your own, answering some basic questions about the discolored board may help you narrow down the problem and resolve it more quickly.


Investigating Solder Mask Discoloration on a Circuit Board

The best way to figure out what the reason might be for your PCB solder mask discoloration is to take two boards that have gone through essentially the same manufacturing process. If one shows solder mask discoloration and the other does not, determining the difference in process between the two might provide your answer.

Did you use a different flux for the discolored board? Was one flux type water-based and the other alcohol-based? Was it manufactured at a higher temperature or with a longer dwell time? Was the discolored board run twice in the pallet? If the discolored board has a different finish or different type of solder alloy, or if it was manufactured with a different thickness or cure cycles, these could all be the culprit.

Other questions to ask include where the discoloration is located. For example — are there white spots all over the board, on the solder mask only or on specific components only? What color are they? Are they white, yellow, black or gray? What do they look like? Milky, granular or smooth? Are they the result of some kind of residue on the board or has the substrate actually changed color? At what point during the process is the PCB discoloration most evident?


Possible Explanations for Discoloration on a Circuit Board

Once you have isolated as much data about the problem as possible, you will probably want to bring the discolored board to your PCB supplier or PCB fabricator for a definitive answer as to why you’re getting solder mask discoloration. However, some of the possible explanations could be:

  • Weather: In some very humid areas, people may see more discoloration on their PCBs. This is not uncommon and not a cause for concern in most cases.
  • Measling: Measling is a phenomenon where you will see little white spots where the fiberglass bundles cross. If your white spots are anywhere other than these intersections, you do not have measling.
  • Delamination: Delamination can occur just about anywhere, and is a failure in your laminating process. If you are experiencing delamination, your board is compromised.
  • Cleaning: If you’re using a chemical solution to clean your circuit boards, your cleanser may be abrasive and damaging your boards.


While there may be other explanations for solder mask discoloration on a circuit board, these are some of the most common.


Avoid Solder Mask Discoloration on Circuit Boards With a Quality PCB Supplier

If you’re repeatedly getting printed circuit boards coming back from your PCB supplier with discolorations — even if they seem to be harmless cosmetic issues — it could be speaking to a larger problem, which is the level of care your PCB supplier puts into making sure you receive high-quality printed circuit boards every time.

Even if you don’t mind a little solder mask discoloration, having a supply that comes from a company without strong quality assurance protocols in place should be of concern to you. Your projects may already be suffering from subpar printed circuit boards without you even realizing it. If this is happening to you, you should change your printed circuit board supplier immediately.


Millennium Circuits Limited for High-Quality, Expert-Tested PCB Products Every Time

Millennium Circuits Limited (MCL) has your solution. We offer all the PCB products you need, from flexible circuit boards and rigid-flex circuit boards to solder paste and IC packaging and more. And you never have to worry about the quality of printed circuit boards and other PCB products we supply. We employ highly trained and knowledgeable technicians to make sure you’re getting state-of-the-art circuit boards for highly efficient products to boost your company’s profile and success.

And quality control is a top priority at MCL. Our expert quality control team puts our products through rigorous in-line testing to ensure compliance, including solderability, visual and mechanical inspections.

No matter your industry, MCL is committed to delivering defect-free PCB products directly to you, on-time, every time, with no minimum orders and top-notch support to address any concerns you may have. We’ve been getting glowing testimonials year after year for the more than ten years we’ve been in business, and it’s because of our commitment to quality and customer service.

If you’re sick of getting printed circuit boards coming to you with discoloration, bowing or twisting or other issues that leave your boards non-functional or non-conforming, put an end to it now and start working with a printed circuit board supplier with an unquestioned commitment to providing quality, customer service and support for your projects and your business.


To learn more, or for a free quote on top-of-the-line PCBs and PCB products for your business, contact MCL today.