In a message dated 3/24/99 11:13:30 AM Pacific Standard Time,
[log in to unmask] writes:

<< Can anyone help me?

 > I have been told by a chip component manufacturer that the reason they
 > changed the pin out on a resistor network from a concave to a convex was
 > because it allowed them to place the pin terminations farther away from
 > one another, which in turn helped to reduce the issue of silver migration.
 >
 > My questions are:
 >
 > 1.  What are the conditions that silver migration can occur?
 >
 > 2.  Could these conditions be present in chip components, particulary
 > resistor array networks?
 >
 > 3.  Has anyone ever heard of this or had issues with this?
 >
 > 4.  Is there any supporting research to back this claim?
 >
 > Thanks in advance for you support.
 >
 > Kathy Palumbo >>

Hi Kathy!

    I've not heard of silver migration issues with chip resistor networks
because of the solder termination design, but I DO KNOW that there will be
more solder problems (solder shorts, misalignment, etc...) with convex ones
rather than with concave ones.

    When I worked for a large memory company we started using chip networks on
the Pipeline Burst Cache' modules we built...there were about 16 or so of
these little jewels on each simm. The difference in first pass yeilds between
the two styles was like night and day...concave ones self-center superbly
during reflow without shorts, while using the convex ones we could expect at
least one short a simm...pretty bad huh?

     The problem is the termination areas that are plated is not defined well
on the actual part. You can look at most of their spec's and they'll have an
illustration that shows that the solderable area is only on a strip centered
up on the convex portion for each resistor, but when you look at an actual
part you'll see plating on the insides betwen each resistor that gives you the
shorts.

     You may have already experienced this problem, and that's why you're
trying to find out why they wanna switch...but I have never heard of the
problem you're speaking of...

-Steve Gregory-

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