Mail*Link(r) SMTP               FWD>FAB/ASSY: Lifted land criteria

Greg,

For the IPC, the RB-276 is the controlling requirements, therefore, there is
no specified limit.

The RB-276 requirement for "no specified limit" is that there is no published
data supporting that lifted lands have led to function failure(s).

In general, from most of the discussions that have been held in the A-600
committee meetings have centered around two issues:

1)  IMO, one of the general feelings is that the lifted land should not be
greater than "one metal thickness" or about 25-35 micrometers.  This is
because there should be a number because if the land were "lifted" at an angle
of 45 degrees to the plane of the printed board's surface "it just wouldn't
look right", and most people would feel uncomfortable accepting such a
condition.  

2)  The second discussion point has been that if the assembly is to be
conformally coated, there may be some contaminants left in the space may lead
to either insulation resistance problems; or the residual contaminants or the
"air void" will lead to possible outgassing or fracturing of the conformal
coating, epecially if subjected to low ambient pressures (aero-space).

Ralph Hersey, e-mail:  [log in to unmask]

--------------------------------------
Date: 7/16/96 12:40 PM
From: Gregg Klawson
Hello!  We're having a discussion here regarding the inspection criteria for
PWB coupon microsection lifted lands after thermal stress.  We're just
cutting over from military procurements to more "commercial" and are trying
to decide what makes sense.  The specifications state:

Mil-P-55110E allows a maximum lift of 0.001 inch.
Mil-P-55110D before ammendment 4 allowed a lift of 0.003 inch maximum.
IPC-RB-276 states "lifting allowed" for all classes (no limit).
IPC-A-600D allows a maximum lift of 0.003 inch.
IPC-A-600E allows a maximum lift of ?????

What is the purpose of this requirement?  Do we need a limit?  If we need a
limit what is the "industry standard" limit from board house and OEM
viewpoints.  We've been calling out IPC-RB-276 class 2 with a 0.001 inch
limit.  A couple of our board houses tell us 0.003 inch is the "industry
standard".  Any and all comments appreciated.

-Gregg Klawson
GTE Government Systems COrp
+1.508.880.1822
mailto:[log in to unmask]

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Date: Tue, 16 Jul 1996 14:47:28 -0400
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Subject: FAB/ASSY: Lifted land criteria
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