Tinting / Plugging ot Test Vias 2

[rossieinexile]

Hi
I am in the process of debugging a pcb as part of the design process. I have two different PCB vendors ( 1 works 1 does not).I have buzzed out the unit that is not working and the PCB seems fine. The only differance between the boards is the one that is working has the Test vias Plugged /tinted with solder mark.
(1) Has any one ever come accross an issue which pluggging the VIAs has made any differance to the functionality of a unit/ circut.

Niall

 

[buzzp]

I have not heard of 'plugging' with respect to vias. Are you saying the vias have solder mask on them on the one that is working and the others don't? It is probably much easier to troubleshoot this from an operations point of view, ie, whats it not doing when its powered up (with the board populated of course) that it is supposed to do? This will lead you to the area where you need to concentrate your efforts. In my experience, the board is generally good and there is a backwards part, solder bridge, bad part, or something else causing the problem. I have seen bad boards as well. Have you tried populating another board and trying it? Also, did you send in the same exact artwork to both vendors?
One other thing is to check that the plating in the vias is there, I have had one case where there was no plating in the vias and this caused nothing to work properly.

 

[Comcokid]

Tenting vs not-tenting a via can make a small difference in high frequency RF circuits. This is because of skin-effect issues, the copper surface Vs tin/lead surface, and the fact the solder mask has a dielectric constant different than air. Also for RF, if an untented via fills with solder, the inductance of the via is affected.

 

[sreid]

Usually the tenting of vias is controlled by the PCB CAD as specified by the designer. If the board fab house created the solder mask they could have tented an electrical pad and it's not soldering. Something else could also be wrong. Have the boards been electrically tested for shorts and opens? Not doing this is to me a false economy.

 

[felixc]

Via plugs have no impact on the PCB performance. So if you're in the design process what you have is two prototypes? Chances are that an assembly bug is at the origin of your problem.