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Solder Mask Bubbling On PCB from Supported Via Holes

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#55501

Solder Mask Bubbling On PCB from Supported Via Holes | 14 July, 2008

I have a board with the above problem from our PCB supplier. After they applied the solder mask and run the PCB's to HASL process, the solder mask bubbled on one side of the PCB making the solder mask thickness higher and PCB looking awkward.

They said they are pushing in solder mask inside the holes during my conversation with them...what is that "pushing in solder mask inside the via" process? is this common way of applying solder mask onto 12.0 to 25.0 mils via holes?

What are the possible causes of the solder mask bubbling during HASL process?

thanks and regards,

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#55530

Solder Mask Bubbling On PCB from Supported Via Holes | 15 July, 2008

Hi Armynski,

I sell for an offshore board house, yes, it is common for offshore board shops to fill vias. The bubble is caused by air entrampment within the hole it self, when heat is applied during Hot air and the via is covered on both sides the entraped air can expand and blow out making the solder mask blister on one side of the board.

Solder mask in via holes is done for two reasons: 1) Board Designer left no solder mask reliefs for the Via's in their design. Which Manufacture would look at as being requested to 100% Via Plug.

2) Via's were requested to be Filled or Tented. Which the Board house would do a second solder mask operation and put a second coat of mask to either fill or cover the Via Pad. This is normally done do to requests by the assembly houses concerned about paste flowing through the Via and puddling on the other side of the board causing shorts. Normally on BGA's.

Typically this operation is not recommended with boards with Hot air due to its extreme temperatures. Recomended would be to leave a blivit or an opening half the size of the drilled hole to allow for no entrapment of air. Or to change surface finish to Immersion Silver or Gold or OSP.

Hope this helped,

Regards, Boardhouse

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#55535

Solder Mask Bubbling On PCB from Supported Via Holes | 15 July, 2008

thanks sir! you explained it very well....

thanks a lot!

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#55561

Solder Mask Bubbling On PCB from Supported Via Holes | 16 July, 2008

Your Welcome.

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