Some pads of the PCB can't have solder adhered, why???

[Erickben]

Hi all, my board has a problem now.Some pads of the PCB can't have solder adhered, we tried to add more solder, but it fails. Could you tell me whether there is a problem for PCB design or craft? we never having any PCB quality problem before. If any one knows, I would be so so grateful.

[Rerouter]

You likely need to use a strong flux to strip off the oxide layer before the solder gets a chance at reaching the metal, to my eye that looks like an older board you are reworking

[nail10]

i also face the same probelm

[Rerouter]

Get some flux (tack / gel / pen) deposit some on the pads, and then heat with an iron tip tinned with some solder (the flux may burn off but it will be refreshed by what is at the joint)

[Eva Liu]

Any contamination solder issues?

[ar__systems]

What is the problem? I see that the pads in question have parts on them, so where is the issue?

[Mechatrommer]

apart from adding flux, there are two more ways you can penetrate the oxide/stray material layer:
1) more heat from a clean iron tip
2) more heat from a clean iron tip

[elecman14]

If you received the PCB from an assembler like that the likely cause is dewetting. Based on how your vias look it appears that you are using a pb free HASL as a surface finish. The way that process works is the board house dips the boards in a molten bath of solder to coat the PCB. If the finish is too thin in those areas you will see the defect. An XRF machine or micro sectioning can be used to determine finish thickness on an un-populated board. Also the solder profile should be validated in that area. Excessive heat could also cause that defect.

If the board has been repaired in that area the defect could be caused by contamination or excess heat.

[technotronix]

Flux!

[mrpackethead]

flux. get some out a delorian capacitor

[KL27x]

Probably some combination of large/thick planes, non-thermal vias, and lead-free solder. Thermal pads, next time, if you want to be able to rework with an iron.

[Tibby]

We once received a batch of boards where the board manufacturer screwed up. They somehow managed to get a very fine spray of solder mask on the pads. Only visible by microscope, but there was no way those pads could be soldered.