Hi Ioan
That is one heck of a lot of questions. Some I'm not qualified to answer, but some I can offer an opinion on - see below. And good luck - writing the answers is much easier than what you've got in store...
regards
Graham Collins
Process Engineer,
Northrop Grumman
Atlantic Facility of Litton Systems Canada
(902) 873-2000 ext 6215
>>> [log in to unmask] 09/10/02 10:06AM >>>
Hi Technos,
badly need your wisdom on this. We have an automotive application, a simple
assembly (single sided reflow + wave soldering) that needs conformal
coating. We are on no-clean CP36 paste from Multicore and X33 no-clean flux
from the same company.
After having browsed last night through the archives, I still have a lot of
questions:
1. what reliability concerns should I have with automotive applications
2. any special coating material more suited for automotive
I'm sure if you specify the environment the chemists on this forum will offer some recommendations. Temperature extremes / vibration / humidity / solvents??? All of these???
3. except for the dendritic growth, any other hazard
4. the Nortel analysis bulletins for both materials show the residues are
inert. should I worry about the flux residues or not? Can the assembly
process make them less inert?
Assembly process can make the residues less inert by ensuring that the flux is applied sparingly and is heated enough to properly activate it. I know of an instance where X-33 was applied in great volume to the top side of a board by an operator using the "more is better" theory of fluxing, with predictably horrible results. Process control is king.
5. if the flux residues are inert, what could screw up the ionic tests?
What kind of ionic tests? And keep in mind that "inert" is a relative thing, the idea behind a no-clean flux is that what is left behind is not harmful in normal use - which is a whole different thing from inert.
6. what cleanliness tests to do and when in the process
Do a cleanliness test on parts before assembly and make sure your process is under control.
7. if fails the test, how to clean
For help with that you will have to appeal to a higher power...
8. how to spec the thickness of coating, how to check it?
We check thickness by measuring an open section of the board before and after coating. Make sure you use the same board, same location. Our spec is 1 to 5 thou thick, obviously that depends on the coating you use.
9. what to expect from a good coating house
10. what is a good test to do for qualification of the sub-contractor. Since
it's the only one in town, how to make him do better?
11. except Concoat and Humiseal, any other major players in the fields?
We use Humiseal products, some others are: Conap, Hysol (Loctite?), Aptek Labs, I'm sure there are more.
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