yes I'm sure that was the problem on a few occasions
Dennis Saputelli
Harry Selfridge wrote:
>
> It sounds like your wave soldering process is not set up correctly. The
> boards should be evenly heated through before wave soldering, then cooled
> uniformly.
>
> What you describe happens when the board is heated mostly on the solder
> wave side, causing softening of the resin and differential expansion top to
> bottom. As soon as the board leaves the soldering station, it is probably
> cooled rapidly by ambient exposure or forced air cooling. This is a recipe
> for guaranteed warping. Your multilayer boards are more tolerant of the
> abuse because they have more thermal mass ( they can't heat or cool as
> rapidly throughout the bulk material ). The inner layers are essentially
> holding things together for you; however, I'll bet the four layer boards
> are also warping - just not as noticeably. If you want to see the physics
> in action for yourself, try taking a scrap board and heating just the top
> side with a heat gun - you'll make a 'Frisbee' of it fairly quickly.
>
> Material, layup, copper volume, and differential temperature are the
> ingredients you need to mix carefully to avoid warp, bow, and twist.
>
> Regards - Harry
--
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