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Looking for expert opinions, Solderability

#29563

Looking for expert opinions, Solderability | 19 July, 2004

We have a need for expert opinions on a solderability issue. Our company prints and then reflows solder paste with no components in place. It is then washed and flattened with a special flattening machine.

Usually, the paste fuses and spreads out to cover the entire surface mount pad right up to the edges. We are running a job that is acting very strange. The solder does not wick out to the edges of the surface mount pads in all areas. Some look OK but many pool in the middle of the pad without flowing at all. The solderpaste is 63/37 and brand new as of this morning. We have tested the paste on another job, different PCB vendor, and it acts as normal so we are pretty sure it is not the paste.

The HASL finish on the PCB's looks different from what we are used to seeing so we would like anyone willing to take a look at some pictures and give us their opinion as to why the paste will not flow on these smd pads. Pictures can be found at http://www.sipad.com/ssi_qa/ssd_question.htm

All opinions are welcome and appreciated.

Matt Kehoe

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#29564

Looking for expert opinions, Solderability | 19 July, 2004

Your fab has supplied you with unsolderable boards. They are dewetted, due to some process problem. That they are dewetted on the annular ring of the via indicates that the problem is with the board and not with your paste. [We assume you do not paste the via area.]

There is an outside chance that these boards dewetted due to a high reflow soldering temperature, but: * ~230*C should not create this type of problem. * Bare boards show dewetting prior to solder paste application and reflow. [Assuming the boards in the pix had not been processed prior to pasting.]

Why does the raw solder paste series of pix appear to have copper colored material on the pads?

Two distressing observations are: * Your board fab's final inspection people stink [are not doing a good job]. * Your company's inbound inspection people stink [are not doing a good job].

Finally, it's fortunate that your final inspection people are doing a good job, because due to your process, it seems like it would be very easy to flatten a blob a solder over an unsolderable pad and never realize it.

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exmaintenanceleader

#29565

Looking for expert opinions, Solderability | 19 July, 2004

okay,

add more flux first and try,

pcb surface is not copper already,

if more flux helps, than your pcb surface should be ok

if not than mehanically cleaning the surface please,

(like your car at home 'pol�roz�s-hungaian' I do not know the english name)

when afther cleaning is ok then you have storeaging problemds or the pcb is not copper (maybe the pcb produer is cange the prduct beore on he's mc carbon or silver or gold or alluminium fingers...and do not clean well he's mashine when your pcb is started)

please let me know your result

szhorvathbp@yahoo.de

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John

#29580

Looking for expert opinions, Solderability | 21 July, 2004

Try to check for solder mask on the pads!

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greg york

#29618

Looking for expert opinions, Solderability | 23 July, 2004

Got to agree with John on this, get a stencil cleaning wipe something a little more potent than standard IPA and wipe the surface thoroughly, this should produce a green residue of solder resist. If this does happen then ask your PCB vendor to look at the extraction on the ovens as resist residue's are depositing back onto the boards Best regards Greg York Tecnical Sales Manager BLT Circuit Services Ltd England

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#29620

Looking for expert opinions, Solderability | 23 July, 2004

I am actually getting opinions that point to contaminated copper under the HASL finish. We've seen some "fish eyes" where the HASL is pulled away from the copper exposing a pin hole of copper that can be seen through the HASL finsh. We are planning on returning these boards to the vendor for solder stripping, copper cleaning, and re-HASL finishing.

Thanks to all for the feedback.

mk

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