Reflow bridging issue

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DaveAK
Posts: 16
Joined: Wed Oct 08, 2008 3:50 pm

Reflow bridging issue

Post by DaveAK » Thu Jul 12, 2018 6:24 pm

I've just completed my first reflow board and I'm very happy with the results. It's just a small board with 3 TSSOPS and half a dozen 0603 caps. I used a hotplate with a piece of 3/8" aluminum plate to spread the heat. All went well but I did end up with three tiny bridges. Two on one chip and one on another. I used a 4mil steel stencil from OSH Stencils.

So what's the best way to remedy these? Exacto knife? Hot air rework? The knife I have, rework tools I don't (yet).

And what's the best way to prevent bridges in future projects? Placing the components isn't easy for me and I wonder if my hands aren't steady enough. Could I be smearing the paste trying to get the chips in place? The next project uses QFN parts and I'm worried that bridging will be more difficult to correct.

Any advice, tips or tricks would be greatly appreciated!

lyndon
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Location: Minnesota, USA

Re: Reflow bridging issue

Post by lyndon » Fri Jul 13, 2018 11:24 am

In my experience, bridging is most frequently due to too much paste being applied. Best way to clean up most bridges on small pitch components is with solder wick. Rubbing some flux on the wick helps too.

DaveAK
Posts: 16
Joined: Wed Oct 08, 2008 3:50 pm

Re: Reflow bridging issue

Post by DaveAK » Fri Jul 13, 2018 2:36 pm

Would a 3mil stencil have been a better choice do you think? I don't seem to do a great job with solder wick, but I've never tried it with flux. I probably just need to practice some more, and maybe get some better tools.

lyndon
Support Volunteer
Posts: 1581
Joined: Thu Jul 17, 2008 6:37 pm
Location: Minnesota, USA

Re: Reflow bridging issue

Post by lyndon » Sun Jul 15, 2018 10:12 am

Possibly, a thicker stencil will hold more paste. I also use the OSH Stencils default thickness. I don't remember what that is, but it works fine with my 64-TQFP devices. I have never tried QFNs.

The "trick" I learned with wick was to use extra flux and make sure the tip of the iron is well tinned, with extra solder even, to get good heat transfer.

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