Peter,

If you have the space to do it, I would suggest increasing the pad size to
about 0.265" square, or, if not, reducing the clip contact area
correspondingly so that you can obtain heel, toe and side solder fillets.
Without these, you are producing stress concentration points that will in
turn cause low peel strength.

Peter




                    Peter Lee
                    <ppwlee@YAHOO        To:     [log in to unmask]
                    .COM>                cc:     (bcc: DUNCAN Peter/Asst Prin Engr/ST
                    Sent by:             Aero/ST Group)
                    TechNet              Subject:     [TN] Pull strength on soldered clip
                    <[log in to unmask]
                    ORG>


                    02/09/02
                    04:17 PM
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                    Peter Lee






Hello,

I ran into an application requiring SMT reflow soldering of a small
copper clip to a pad. The resulting solder joint was so weak that a
slight pull on the overhanging lip will rip off the entire clip from the
pad. I examined the mating surfaces afterwards and both were still
solderable.

The 0.005" thick clip has a flat 1/4"x1/4" surface which was placed
right on top of the pad with the same size. Stencil aperture is 1:1 and
both the pad and clip have good solderability (before and after). The
rest of the components on the boards are soldered well. I like to know
if there is a way to determine how much pull strength should I expect
with such design? In order to strengthen the solder joint, does it make
sense to increase the size of the pad to ensure wetting on the edge and
force excess solder to flow on top of the clip?

Any advice is appreciated.

Rgds,
Peter



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