One of the issues we found which was causing this problem, cracking of TSOP
packages was the pad design.  The pads were too long and extending beneath
the component body.  When the solder joint was created there was no stress
relief in the joint and hence the beginning of the cracking solder joint
problem.

The pad layout should extend the inner dimension of the pads to be further
apart than the width of the component body.

Hope this helps.

Leo Lambert
EPTAC Corp.
Bedford NH.
[log in to unmask]

At 05:13 PM 10/7/96 -0400, CINDY KEMP ORLANDO ISC 8*826-6873 wrote:
>
>
>From: [log in to unmask]
>Date: Mon, 7 Oct 96 15:59:36 EDT
>Message-Id: <[log in to unmask]>
>To: [log in to unmask]
>Sender: [log in to unmask]
>Precedence: bulk
>
>Does anyone have experience with Surface Mount Soldering plastic TSOP
>packages?
>
>We are experiencing cracks in these SMT TSOP solder joints.  The cracks
>start in the heel and propagate to the toe of the solder joint.  
>Initialy these cracks were observed after the convection solder 
>operation.  We then reduced the amount of solder (6.5 mil height) 
>and the temperature of the solder operation (205-210 C).  Although
>the solder joints looked good after the SMT process they did crack 
>after the subsequent wave solder process.
>
>The leads of the TSOP device are Alloy 42 (Kovar) fine 19.7 mil pitch.
>The PWB material is Multifunctional Glass (Tg 180).
>
>Edward Karnish
>Lockheed Martin Communication Systems
>[log in to unmask]
>phone 609-338-3182   
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