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

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


Pad Design

Jacob

#5964

Pad Design | 16 April, 2001

Please help, Engineering has come to me with a crazy idea of putting vias straight through 0805 pads due to limited board space. I was wondering if this has ever been attempted by anyone and if it works. I'm assuming it will have negative affects on the reflow process,please any information on SM pad design will be greatly appreciated also if any one has tried this before I would love to know what the outcome was. Thanxs a bunch, Jacob Lacourse

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#5965

Pad Design | 16 April, 2001

Been there, done that, don't wanna do it again.....

Was lucky enuf one time to recieve a customer PCB ( we were a contract house, nuff said...) where the PCB designer had decided to put vias in the pads of a QFP80. Probably don't hafta tell you that it was a touch up nightmare. Solder is prone to gravity just like anything else, so the first place all your solder flows is right down that hole. Once the hole is filled, you might be lucky enough to have enough solder left for a fillet, but I doubt it. SO, your boards are off to touch up land....

Long and short of it, make em suffer and put the vias somewhere else.

Phil

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genny

#5966

Pad Design | 16 April, 2001

Happened at my company lots on our older designs. We touched up those pads in house by hand, because the solder joint was very poor. We also did it on SOT 86 pkgs on the gnd pins. When they were touched up, we would get an extra 1/2dB of gain out of the device. We have finally changed that layout. Recently we had a design that needed good heat transfer from a heat slug on the bottom side of the device thru the PCB to the heatsink. It was suggested that we use lots of very small holes - 13.5mil - directly under the device. About half the holes stay filled. There is a chance that not all the solder will drain away, if a very small hole is used.

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Michael Parker

#5967

Pad Design | 16 April, 2001

If, after all the good advice already given, the engineer insists on following his wacky design, you may still be able to influence some success.

First you have the fab house plug the via holes with solder then you make sure that the bottom side of the via is tented with solder mask.

This can minimize the potential for touch up.

Only do this if there is no way out of the design.

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Dason C

#5969

Pad Design | 16 April, 2001

Consider to use micro via 10 mil or less, it may help to prevent any solder/flux reflow to the other side and affect your next printing operation. Also, solder void need to be under consideration.

Dason.

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#5971

Pad Design | 16 April, 2001

PCB X-Ray Inspection