Phil
Welcome to Board Talk. This is Phil Zarrow and Jim Hall, the
Assembly Brothers. What do we have
today?
Jim
A very generic
problem, but it's very detailed. We
are having continual lead bridging problems with our wave soldering
system. How would you
rank the following most likely and least likely causes and areas to
investigate?
Here's the list: flux quantity; flux type; solder pot
contamination; solder pot temperature; component angle through the wave; wave
solder ramp angle; and other.
Remember, when your leads are in the pot, you have 100 percent bridges. Now, you're counting on the weight of the solder to cause the bridges to fall off. If the solder is too cool, the viscosity is too high, that doesn't happen.
Then the one
that isn't on the list is preheat profile.
The flux has got to be preheated properly. You have to make sure it's fully activated,
but not preheated so much that the activators are burned up and you get
re-oxidation, because you're counting on your
flux to hang around in the wave so that it helps the bridges to
flow off.
Phil
There are a lot of
other factors like pad spacing, the
length of the leads, the design.
If you've got bad pad spacing that's outside of the IPC guidelines, you're going to have bridges. If you're trying to wave solder some of these new connectors with 40-mil pitch or 25-mil pitch, you're also going to have bridging problems.
You may want to go to a selective soldering.
Phil
These are all important parameters that have to be controlled, whether they're affecting bridging or not. So, they should all be controlled including solder pot contamination. It may not affect the bridging but you better have that under control.
Jim
All of these things could contribute to bridging, so it's a good list. I think we've given you some input on what we feel is important, but check them all.
Phil
This is Phil Zarrow and Jim Hall ...
Jim
Saying don't solder like my brother.
Phil
And don't solder like my brother, and watch for him under those bridges, too.
If the layout of your product allows, have a pallet designed with the product image rotated. The goal is to orient to provide the greatest amount of separation between connector leads as they travel across the wave.
I've used ~27 degrees on most dual row headers in our designs, but this could vary for your product. Also, order your pallets square, if possible. This provides flexibility to turn the product when responding to problems.
Ken Daniels, Process Engineer, Zhone Technologies