Printed Circuit Board Assembly & PCB Design SMT Electronics Assembly Manufacturing Forum

Printed Circuit Board Assembly & PCB Design Forum

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Plugging of via through holes

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#55643

Plugging of via through holes | 23 July, 2008

Hello, We are using a PCB with thickness 3.2mm 4 layer and lot of through hole via's of diameter 0.4mm.

We specified our PCB vendor to do plugging.

Now we have big problems, that after 1..4 weeks we measure a low resistance between track's/via's of 20..60kOhm (unstable resistance).

We found out, that the PCB vendor is using his normal solder resist for plugging of via-holes.

Questions: - Is this a standard process for plugging? - Is this okay for such thick PCB's or is it mandatory to use a special plugging paste? - Could the low resistance problem be caused by uncured solder resist in the via hole?

Best regards G´┐Żnther

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#55645

Plugging of via through holes | 23 July, 2008

Q1. Is this a standard process for plugging? A1. Not as such. We checked both IPC-6012 and IPC-SM-840. Neither comments on plugging. So, your fabrication notes rule the day. Q2. Is this okay for such thick PCB's or is it mandatory to use a special plugging paste? A2. What ever works is OK. This doesn't work. The aspect ratio limit for plugging is 6:1, for most fabs. Your boards are 8:1 [assuming the 3.2mm thickness and via diameter of 0.4mm are finished numbers]. So, your board thickness is not pressing the state-of-the-art. Q3. Could the low resistance problem be caused by uncured solder resist in the via hole? A3. As you, we expect this resistance to be hundreds of megohm. It's reasonable to question the cure of the plug material. What is the cure mechanism of this solder mask? It there a secondary cure?

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