Practical BGA rework—the simple way forward with POP paste
Bob Willis
Practical BGA rework—
the simple way forward
with POP paste
As many engineers and rework staff know,
there are a wide range of techniques for
replacing BGA components on a board
assembly. You can use a tack flux, a mini
stencil for printing paste on to balls or
the substrate. Alternatively, you can use
adhesive polyimide stencils, performs, the
list goes on and on. The key factors are the
success of the process and the quality and
reliability achieved on the final product.
Equally important is the right volume of
solder for the joint, which can vary depend-
Figure 1. POP paste on BGA balls prior to reflow to Figure 2. POP flux on BGA balls prior to reflow to
ing on the BGA ball material and low or the surface of the board. the surface of the board.
high temperature parts.
A couple of years back, I started playing
around with STACK or package on pack-
age (POP) to better understand the process
and problems faced. This was suggested
due to the high number of people asking
about overcoming warping during reflow
at my Process Defect Clinics sponsored
by IPC and Productronica in Germany.
It seemed the industry all had the same
problems at once. At that time a tack flux
was commonly used for the upper package
connection rather than paste.
What has become very common
practice in board assembly now seems
like a simple rework technique. I am still
surprised that there has not been a flood of
suppliers offering dip paste for rework. Are
marketing departments in the planning
stages, or has the recession held back the
launch of innovating products?
Stepping through the process of dip
paste in a rework application may look
something like this:
Figure 3. Unqualified rework operator Bob levelling the paste on the glass slide prior to dipping the balls in to
the solder paste.
4 – Global SMT & Packaging – June 2009 www.globalsmt.net
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