In a message dated 6/5/98 6:01:15 PM Pacific Daylight Time,
[log in to unmask] writes:
> Hi
>
> Is there anyone who can give me an advise regarding the no solder
> problem I encountered on my board. It always occur at transistor,
> sometimes it does not have any solder after passing the solder wave.
> I already conducted different loading orientation just to know what
> is the rootcause of the said problem, but still no solder.
>
>
> Other problem, the chip capacitor crack after wave soldering .
> Kindly give me advise on how to prevent this problem.
Hi Aura,
Well, there's many different reasons that could cause the no solder
problem on the SOT's. When you said you changed the orientation, what exactly
did you do? Did you turn the board so that the leads wouldn't be shadowed by
the component body? Like this:
_ _
|
__|_|______|_|_
|
| | Direction of travel
| WAVE
| ____________ | ------------------------>
|
|_|
|
Assuming you have a solderable board and parts, then the next thing I would
look at is the wave solder profile. It could be that the preheat isn't hot
enough, which could possibly be causing both problems with the capacitor and
the SOT.
If the preheat isn't hot enough, the flux isn't activating the way it should
causing the solder to not wet properly, and the low preheat is giving your
caps a heck of a thermal shock when they hit the wave. The board should be
have a temperature plot done to make sure the profile is set right. One thing
you can do to just give a simple check and see if the profile is kinda' close,
is to stand right by the wave as a board starts across it and listen for a lot
of sizzling and popping noises...like bacon frying. If you hear that, you can
be pretty sure that it's on the cool side and needs more heat. The flux on the
bottom of the board shouldn't sizzle and pop when it hits the wave, maybe a
very slight hiss...but that's about it.
One other thing I thought about that might give you the solder problems on the
SOT's. I occasionally would find out that one of the operators would sometimes
just use a Kimwipe or something to wipe the epoxy off the boards when they had
a rejectable epoxy dispense job, instead of thouroughly cleaning the board
with a solvent. They can wipe it to where it looks clean, but there actually
is a very thin coating of epoxy on the pads that's next to invisble. For some
reason, it seemed the SOT locations wouldn't solder if they did that, but
almost everything else soldered okay...but you might want to check that mis-
dispensed boards are being cleaned properly.
-Steve Gregory-
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