hi,

if you've covered over the solder joint with metal, where do you expect entrapped gases to go?  i'm not sure what your process details are, but we experienced the same problem when using solder paste with leadless ceramic chip carriers.  the problem went away when we separately bumped the board and the lcc with solder then reflowed the two with a very minimum amount of paste flux.

i'm sure you hear from some who will wonder why you care about voids anyhow.

phil

-----Original Message-----
From: Jonathan A Noquil [mailto:[log in to unmask]]
Sent: Friday, May 11, 2001 2:56 AM
To: [log in to unmask]
Subject: [TN] Solder Voiding


Hello Everyone,

Please help,
Can Anybody explain why too much voiding
occurs when two metal is joined (Top Metal
and Bottom metal)? Eventhough the peak temp is
40 C over than the liquidus temp of the solder.
When a solder is reflowed without top metal
the solder wetting is very good and the appearance
is shiny. But when you put a top metal to be joine
and then X-ray, there are a lot of voids.
I tried to removed the top metal, and the picture
below showed a lot of voids. Another thing is the
color is not shiny but grayish.




(Embedded image moved to file: pic29915.pcx)

The paste is 85Pb/10Sb/5Sn
Peak temp is 290 C
Oven: Conduction
Time until the unit is out: 180 Seconds.


Many thanks to everybody.

Sincerely
Jonathan

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