[log in to unmask] asked

Is there a standard for the distance between SMD components in the wave
soldering process to prevent shadowing?   We are currently basing it on 1.5
times the component height.  What is the shape of the  "deadspace" behind
these components, rectangular, conical, oval... ?

Any help is greatly appreciated.

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Dean,

Several people will give you a good "rule of thumb" for your question.
However, I would suggest that you follow good engineering practice and
determine what your customer can tolerate (that's the process boys in the
factory).  Many years ago I assisted a couple of engineers from a company
whose design group had created an SMT wave solder design study PWB.  The board
started at one end with typical component layouts that gradually tightened in
spacing as they moved to the other end.  The objective was to try and
determine the smallest spacing that still soldered without defects.  The board
was sent to all of the companies factories to determine what the limits of the
current factory processes were, with the intent to design only what could be
built.

Many of us offer comments about design rules, saying how we use them day to
day, without specifying the particulars of our process.  The equipment,
stencils, fluxes, solder pastes, etc... are all important parts of the process
and directly impact the design rules.  Just as important, in the wave solder
SMT case, will be the shape of the lands used.  The use of longer but narrower
lands and selective use of robber pads will also impact the manufacturability
of the design.

For some good reading, try         http://www.avxcorp.com/tech/smt.htm

Steve Mikell
Lead Ind. Eng. Plt 13
SCI Technology

PS:  to finish the story of that design study, the SOTA wave solder systems we
tested soldered 100%, except where part misplacement issues were present.  I
do not currently have a copy of the design spacings, but that was 1990 data
anyway.

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