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

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


Reflow Problems

Views: 1661

SWAG

#46448

Reflow Problems | 3 January, 2007

We have a SMT build that has been trouble from day 1. This board is about 2" x 2" and is panelized. The PCB is unusually thick (0.100"). The problem we always have (no matter if it's leaded or no-lead) is that the solder likes to wick up the heal of the leads on many of the parts. (Most of the trouble parts are miniSOT's). Due to the thickness of the PCB + small parts, it's hard to equalize the temp. between leads and board surface. We have tried new stencils and messed around with reflow changes with limited improvement. Does anyone have advice on what to try??? Thanks -

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#46449

Reflow Problems | 3 January, 2007

What I would suggest trying is to only use your bottom heaters in your oven. In this way the board will receive the majority of the heat and conduct the heat to the component. Since your components are small and your board is more then twice the standard thickness I believe this would be the appropriate method for this build.

Good luck, Patrick

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#46469

Reflow Problems | 3 January, 2007

Your component leads are getting much hotter than the pads on your board. Slow down the conveyor.

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#46479

Reflow Problems | 4 January, 2007

davef is correct. The solder is indeed wicking to the hottest part of the leads. Slowing down the conveyor will alloy the board and component to come to temperature at a lower delta T.

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Jnet

#46766

Reflow Problems | 17 January, 2007

Agree. Drop the conveyor speed.....and drop the zone temps accordingly. This should allow the board leads and components heat at a more even rate and stop the over temp. issues. I do not suggest running only the bottom heaters this can bring new issues into the loop.

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#46772

Reflow Problems | 18 January, 2007

Good afternoon,

Profile your oven. Try to increase soak zone as much as possible. This must equalize temperature across the board and leads to prevent wicking. �Spike� as slow as possible after long soak. Do you use tooling for this PWB in production? Improper tooling could create issues as well.

BR, Pavel

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SWAG

#46790

Reflow Problems | 18 January, 2007

Thanks for your advice, all. We do not use tooling, Pavel. We requested a board thickness change from our customer - it turns out that the unusual thickness was designed for mechanical fit-up only and this thickness is no longer a concern as the assembly design has changed. Who knows if we'll get this, though. For now, I will further experiment with profile changes per everyones advice.

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#46820

Reflow Problems | 19 January, 2007

As a sidenote, if nothing of the above works, IPC 610 states that it is accetable (class 1,2,3) for solder to touch a SOT body if it is plastic.

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Reflow Oven

reflow oven profiler