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Soldering an 18 layer 2oz. copper board

mike m


Soldering an 18 layer 2oz. copper board | 18 October, 2002

We are currently experimenting on an 18 layer 2 oz. copper backplane. The spec is calling for 100% solder joint top to bottom. Any input greatly appreciated.

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Soldering an 18 layer 2oz. copper board | 18 October, 2002

Big BIG BIGG wave with a lot of preheat capability both top and bottom. You may need to exceed the standard "100 C" top side preheat to 120C or so (be aware of any topside SMT going into reflow over the wave). A spray fluxer with very fine atomization and may still require top fluxing. Make sure P.T.H.s are fairly large roughly .03"to .05" larger than diameter of leads. use the minimum trace widths with the wagon wheel pattern on all holes being tied to ground. Run the wave as deep as you can.

rub belly, tap head, find a good chant to perform prior to waving.

Just out of curiosity why the 100% fillet requirement?

Good luck!! Russ

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Soldering an 18 layer 2oz. copper board | 20 October, 2002

Like Russ, I am also curious about the 100% fill requirement.

On any thick, high mass board the key is getting as much heat as possible into the board. If you get the board to the proper temperature, solder will flow just about anywhere.

As an alternative to a large wave you could use a dip soldering system. The basic advantage being that the static solder pot in a dip system allows large amounts of heat to be transfered quickly to the entire surface of the board.

I recently worked with a customer on a similar MIL-spec backplane and we were able to meet a 75% fill spec easily. We did acheive 100% fill on some holes, but since that wasn't the spec we didn't really keep tabs on how many.

We found that the preheat stage was critical during the process. This will be true whether you use our system or a wave. I agree with Russ that you will probably need to look for 120C, thats the number we used and it seemed to work well.

If you would like any more information please drop me a line or give me a call at 714-672-9944.

Stephen Pence VP-Engineering Unit Design, Inc.

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Soldering an 18 layer 2oz. copper board | 21 October, 2002

Mike, We are currently wave soldering several assemblies with with a lot of ground plane. The soldering handbook we have in house suggests a preheat temp for metal core multilayer boards of 230 to 270 degrees F' (110 to 130 C'). It was scary at first heating the boards this hot, but it works pretty good. We have both top and bottom preheaters, and have only had a problem heating up the boards that have a tinned surface front and back. I also always add some flux on top for good measure. Good luck.

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Soldering an 18 layer 2oz. copper board | 21 October, 2002

Mike, If your wave solder machine doesn't have enough preheat capacity you can put the board in an oven and warm it part way before you put it into the wave solder machine.

This works best with a spray fluxer, as a warm board will collapse the foam head on a foam fluxer. If you have a foam fluxer, just turn it off and get yourself a spray bottle and hand spray the board as you put it on the conveyor. I've done that, and used a hot air gun try and keep the board from cooling any before it gets to the preheaters.

Good luck, Mike F

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