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Solder Balls @ the Wave Process

#18278

Solder Balls @ the Wave Solder Process | 27 November, 2001

Solder balls on the topside of our wave solder boards is a real issue. We have found that during the wave solder process, solder will enter through the via holes in the form of solder balls. It seems to be related to flux captured in the vias and once the wave hits there is a splattering effect. The problem seems to be greater at times. I have asked design for some options with these plated through holes but haven't found any. The vias are used as test points in most cases. Does anyone have any suggestions?

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Michael Parker

#18279

Solder Balls @ the Wave Solder Process | 27 November, 2001

Short term fixes can be:

have the vias "plugged" with solder by the fab house. This works if your fab is HASL finish. Tent the vias with solder mask, top side only. You may get a flux entrapment issue in the vias with this manner.

Long term fix can be: Have the designer specify test points instead of open vias. Can the vias be "blind" on the top side?

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Ken Lester

#18281

Solder Balls @ the Wave Solder Process | 27 November, 2001

Options that may help. Do you use a Vibratory Wave if so try reducing. The solder temperature shouldn't be to high. I would suggest 485F but is process dependant. Try slowing the preheat cycle this also may help. because this is variable I would try a little slower conveypor speed aperhaps 10 to 20% reduction first.

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#18291

Solder Balls @ the Wave Solder Process | 27 November, 2001

Search the fine SMTnet Archives on the topic to get started. For instance: http://www.smtnet.com//forums/index.cfm?fuseaction=view_thread&CFApp=1&Thread_ID=1861&#Message7671&

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Don Burr

#18382

Solder Balls @ the Wave Solder Process | 9 December, 2001

It sound you have already discovered to root cause, flux entrapment in the via holes. Short of changing the desing, here are sone suggestions. The main thing is you have to dry out the via holes of the wet flux. Some things to try are: slow down the conveyor speed so there is more drying time in the preheat. You may have to lower the pre-heat so as to not over heat you board before entering the wave. You can install force convection pre-heaters to improve the effiency of drying the board before entering the wave. You can (install if you have a spray system) turn up the velocity of the (foam) fluxer air knife to help blow out the excess flux out of the via holes. You want to have a 30 degree angle on the air knife holes relative to the board. This angle helps create a gentle turbulance of air velocity that put out the excess without blasting all the flux out of the hole.

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