Hello Michael,
You seem to be in a strange situation. Calling for a leakage test spec
for a part which is not a hermetic part, that's strange. In our company
we use to regard components as either hermetic or non-hermetic. If they
are hermetic, organic sealants are not actual, only metallic sealings
are relevant(soldering, laser welding, seamwelding etc). So my first
reaction is that your parts should be made true hermetics, if that is
what you want. A little more expensive material selection, but in the
end it will save money for you. If your application is a Hi-Rel one,
true hermeticity will do fine.
If, on the other hand, your product is a massproduced part for a more
shortliving demand, I understand that true hermeticity is too exclusive
for you. In that case I would recommend you to stop cleaning in water
and make the process window such, that you can rely on the glueing
procedure. You may just do some statistical random tests when the
adhesive application is within the process window. Then, if your
customer does not require a leakage test, don't do it!
Maybe not the answer you wanted to hear, but it's not easy to get the
whole picture.
Good Luck! //Ingemar
----------------------------------------------------------------------
> We are seeing problems with water getting into our hybrid ICs
during
> aqueous cleaning. The substrate is made of alumina as well as the
lid.
> The substrate is 1.5 in. square. The lid is 1.45 in square with a
wall
> thickness of .050 in and height of .105 in. At first we used Kyocera
NC0150
> B stage epoxy to attach the lid to the substrate. What we found was
cracks
> in the epoxy. We then tried RJR poly RJ4B, but failed because of
leakage
> problems during the leakage test (submerge the part in a liquid and
look
> for gas bubbles). We then tried RJ9F epoxy which started to have fine
gas
> bubbles all around the seal after 30 seconds.
>
> We started seeing problems with our Hybrid ICs shorting out
internally
> due to water getting into them during aqueous cleaning. What we found
is
> that if we hand solder the parts on the board and then send the parts
> through the aqueous cleaner (Westek Inline Triton IV ) the parts are
fine.
> If we sent the parts through a convection reflow process ( Heller
1500SN) ,
> wait until the the board has cooled down, typically 5-10 min., then
send
> the parts through the aqueous cleaner we have leakage problems. These
> parts are fine pitch devices and hand soldering them is very time
> consuming! The parts are mountied on a .092, FR4 PCB approx. 12 in X
18
> in. with surface mount and through hole connectors (paste-in-hole).
>
> Does anyone have any ideas on the problem may be or a possible
solution?
> We would like to call out a leakage spec. for the part but I,m not
sure
> what the spec. needs to be to go through convection reflow and aqueous
> cleaning, any ideas? I would welcome any comments. Thank you in
advance.
>
> Michael Forrester
> LeCroy Corp.
> [log in to unmask]
>
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