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1996

DesignerCouncil@IPC.ORG

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From:
"BELLLES" <[log in to unmask]>
Date:
Fri, 21 Jun 96 10:13:18 MST
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Hi Fred,

          I will keep it short, and only reply to one of the topics...

          >SMT Components on the Solder-side of a PWB...

          The one issue that I haven't seen anyone f/b to you yet is
          utilizing 1206 0.1 uF caps on the solder-side of a PWB that
          will be processed using Wave-Flow soldering process.

          We have had many failures in previous years with bottom
          mounted .1/1206 caps, where they have been fracturing from
          the heat cycling of the wave solder.  After extensive
          cross-sectioning, and intense Vendor work, we found that the
          massive layer count in a .1/1206 (& sometimes an 0805) was
          the Culprit. Just too much packed into a small area.

          These problems were solved by either reducing the values to
          a .01 or a .047uF cap, or by duplicating caps where you
          still needed the higher capacitance.

          I know that we have since discovered that most vendors have
          resolved these issues with their discretes, but we decided
          it was much safer to design away from this value where
          possible. This reduces the chance of a low quality vendor
          being selected that may still have potentially poor part
          integrity.

          hope this helps...
          Les Beller
          EchoStar
          "DISH Network...
          ...Where everthing comes on a dish"
          ([log in to unmask])



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