4 ms·

Agree. For example, changing solder mask color can affect component placement accuracy and solder bump size.

by kurthr 4y ago

0_____0 4y ago
??? IME soldermask is pulled back from the pad generally unless you're doing soldermask defined pads for things like BGA. Plus, the fab generally modifies the pullback themselves. My soldermask layer is pretty much just 1:1 with the pad outline, if I want a particular pullback I would specify that in the fab drawing. I can't see how soldermask color would affect placement either, especially not if you place fiducials (or if the fab places them for you!)
- katmannthree 4y ago
  Pigments can affect the properties and behavior of resins, if you're working with a sloppy fab I could see that causing issues (even if only not accounting for different curing times). For actual production design like the OOP is talking about, you would likely go with whichever option is cheapest overall (which in my experience has universally been the standard green).
  - kurthr 4y ago
    Exactly, if you're hand soldering through hole components, it's not a big deal. However, blue/black/white solder mask pigments were noticeably (>2mil) smaller in tests than the standard green for a high volume manufacturer. Most of the time a partially mangled pad reflow wouldn't be a problem, but when you're automatically stuffing the boards, you won't know and could have latent failures (temperature/time) after production test. This is especially the case for aQFNs and BGA ICs. Fiducials are automatically placed in top copper, but we also noticed larger misalignments of paste and smaller 01005 passive components (pre-reflow) on non-standard colors. Again, unlikely to cause large yield problems unless you've got a lot of components, but why risk it. We did still use red for test PCBs so that they wouldn't be shipped to customers. If we were making gaming video cards colors would have been more of a priority.
bsder 4y ago
Let me counterexample where changing soldermask is good: In my experience, changing from Green Soldermask (everybody's default) generally gets you better soldermask coverage as they aren't trying to optimize usage to the micropenny. If I want mega-cheap, green is good. If I want reliability, almost any other color is better.
- doug_life 4y ago
  I love seeing hardware posts on here. I often use colors other than green to differentiate revisions, however green typically has the smallest minimum web requirement which makes a difference on high density designs.
  - bsder 4y ago
    Hmmm, never thought about that. I don't think I've noticed a different minimum web requirement based on color for 0402-class and QFN stuff, but I could certainly believe it for extremely small footprints and high-density BGAs. Where I seem to see issues with green soldermask coverage are tented vias underneath components. The canonical example is a non-GND via underneath a QFN component with a pad. However, I have also seen issues with vias next to large pads of power transistors where the transistor can "float" around on the solder. This seems counterintuitive since I would expect the main soldermask color to be used for more BGA-type components where the breakout vias would need to be covered properly. Nevertheless, experience suggests otherwise. I finally got fed up once and ordered the same PCB with green soldermask for one batch and blue for another. The green ones had some via coverage fails; the blue ones didn't have any. Since then, I've just avoided green soldermask unless I'm going for uber-volume levels of PCBs.

Agree. For example, changing solder mask color can affect component placement accuracy and solder bump size.

by kurthr 4y ago

Agree. For example, changing solder mask color can affect component placement accuracy and solder bump size.

??? IME soldermask is pulled back from the pad generally unless you're doing soldermask defined pads for things like BGA. Plus, the fab generally modifies the pullback themselves. My soldermask layer is pretty much just 1:1 with the pad outline, if I want a particular pullback I would specify that in the fab drawing. I can't see how soldermask color would affect placement either, especially not if you place fiducials (or if the fab places them for you!)

katmannthree 4y ago
Pigments can affect the properties and behavior of resins, if you're working with a sloppy fab I could see that causing issues (even if only not accounting for different curing times). For actual production design like the OOP is talking about, you would likely go with whichever option is cheapest overall (which in my experience has universally been the standard green).
- kurthr 4y ago
  Exactly, if you're hand soldering through hole components, it's not a big deal. However, blue/black/white solder mask pigments were noticeably (>2mil) smaller in tests than the standard green for a high volume manufacturer. Most of the time a partially mangled pad reflow wouldn't be a problem, but when you're automatically stuffing the boards, you won't know and could have latent failures (temperature/time) after production test. This is especially the case for aQFNs and BGA ICs. Fiducials are automatically placed in top copper, but we also noticed larger misalignments of paste and smaller 01005 passive components (pre-reflow) on non-standard colors. Again, unlikely to cause large yield problems unless you've got a lot of components, but why risk it. We did still use red for test PCBs so that they wouldn't be shipped to customers. If we were making gaming video cards colors would have been more of a priority.

bsder 4y ago

Let me counterexample where changing soldermask is good: In my experience, changing from Green Soldermask (everybody's default) generally gets you better soldermask coverage as they aren't trying to optimize usage to the micropenny. If I want mega-cheap, green is good. If I want reliability, almost any other color is better.

doug_life 4y ago
I love seeing hardware posts on here. I often use colors other than green to differentiate revisions, however green typically has the smallest minimum web requirement which makes a difference on high density designs.
- bsder 4y ago
  Hmmm, never thought about that. I don't think I've noticed a different minimum web requirement based on color for 0402-class and QFN stuff, but I could certainly believe it for extremely small footprints and high-density BGAs. Where I seem to see issues with green soldermask coverage are tented vias underneath components. The canonical example is a non-GND via underneath a QFN component with a pad. However, I have also seen issues with vias next to large pads of power transistors where the transistor can "float" around on the solder. This seems counterintuitive since I would expect the main soldermask color to be used for more BGA-type components where the breakout vias would need to be covered properly. Nevertheless, experience suggests otherwise. I finally got fed up once and ordered the same PCB with green soldermask for one batch and blue for another. The green ones had some via coverage fails; the blue ones didn't have any. Since then, I've just avoided green soldermask unless I'm going for uber-volume levels of PCBs.