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

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


Dummy Pads for Bridging Problems

Todd N

#15933

Dummy Pads for Bridging Problems | 11 May, 1998

We are having continuous bridging problems with the trailing leads on a 26-pin D-sub through-hole connector. The pitch is 0.100". The connector is going through the wave at approximately a 20 Degree angle. Does anyone have any board layout recommendations for size,location,spacing, and # of dummy pads/holes to eliminate this bridging problem. Thanks.

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Steve Gregory

#15936

Re: Dummy Pads for Bridging Problems | 11 May, 1998

On 11 May, 1998 Todd wrote: | We are having continuous bridging problems with the trailing | leads on a 26-pin D-sub through-hole connector. The pitch is | 0.100". The connector is going through the wave at approximately | a 20 Degree angle. Does anyone have any board layout recommendations for | size,location,spacing, and # of dummy pads/holes to eliminate this bridging | problem. | Thanks. Todd, Dummy pads for a thru-hole component? Hmmmmm,...I don't think I've ever seen dummy pads for thru-hole before. I think mainly because there's a different kind of wetting force going on with PTH leads than what's happening with SMT leads...and to tell ya the truth, I don't know if that would even work. There's gotta be something else going on that's causing you to bridge like that. One thing with the design that could be causing problems is that the leads that are bridging are connected to an internal power or ground plane and not thermally relieved, the internal plane acts like a heat sink and causes the solder to freeze and solidify before the solder has a chance to separate cleanly as it's exiting the wave. When was the last time you had a solder analysis done on yer' pot? It doesn't take a whole lot of contamination of other metals to make the solder behave weird. Just a little too much copper, aluminum, etc. can change the liquidous point and viscosity, not to mention the grain structure of solder joints. Just out of curiosity, what kinda process are you in, no-clean or water soluble? What kinda' wave ya' got, and what sorta set points are ya' runnin? Ya' know, belt speed, pot temp, preheat, yada, yada, yada... -Steve Gregory-

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Chrys

#15935

Re: Dummy Pads for Bridging Problems | 12 May, 1998

| We are having continuous bridging problems with the trailing | leads on a 26-pin D-sub through-hole connector. The pitch is | 0.100". The connector is going through the wave at approximately | a 20 Degree angle. Does anyone have any board layout recommendations for | size,location,spacing, and # of dummy pads/holes to eliminate this bridging | problem. | Thanks. Teardrop shaped pads. I recall running a DOE many, many moons ago on just this topic. The winner for dummy pads for d-subs was teardrop shaped. The point going towards the pin. I can't really recall any more details like size or spacing 'cause it was about eight years ago, and since then we've gotten hot air knives on our waves and haven't had any problems. Hope this helps. Sorry I can't remember more.

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Bob Willis

#15934

Re: Dummy Pads for Bridging Problems | 7 June, 1998

Dummy pads can work well on through hole parts and are often used in the Far East and on IBM products. If you take a VCR or TV board you will often see this trick being used. Alternativly you can stagger the pads at the trailing edge that works well. Another nice fixit in the short term is have your process engineer on glue dispence put a dot of glue between the through hole pads all your problems will go away. Design rules on drainage pads on through hole are on my video tape on DFM details on my web page www.bobwillis.co.uk

| We are having continuous bridging problems with the trailing | leads on a 26-pin D-sub through-hole connector. The pitch is | 0.100". The connector is going through the wave at approximately | a 20 Degree angle. Does anyone have any board layout recommendations for | size,location,spacing, and # of dummy pads/holes to eliminate this bridging | problem. | Thanks.

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