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If you observe white patches on a PCB, dark stripe PCB solder mask discoloration or some other type of solder mask discoloration? And solder mask discoloration on a circuit board will affect the performance and the quality of the finished boards. Check this passage ad we will tell you everything about it. What are the causes and how to prevent it?

Why solder mask discoloration is dangerous?

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.

How to investigate solder mask discoloration?

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?

What are possible explanations for discoloration on PCB?

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.

How to avoid solder mask discoloration?

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.

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