Shear testing of BGA pads—pads are not as good as they were?
Figure 3. Results of shear testing on balls after the initial reflow. With one rogue
Figure 4. Results after a second reflow operation on sample panels. The results on
result, the FR4 laminate provided the highest shear force results.
FR4 still have the higher shear force results.
Figure 5. Examples of the type of failure seen during the testing. First shows copper pad separation from the laminate, the most common failure. Second example shows joint
failure and the third shows pad separation.
or alternatively the highest cohesive It is well known that the copper pad
Bob Willis is a process engineer working in
strength within the laminate, such that strength has been found to be weaker on
the electronics industry, providing training,
failure generally occurs in the solder. In modern laminate materials, this is high-
consultancy and product failure analysis. Bob
both high TG lead-free recommended lighted by the increased incidence of BGA
also offers on site workshops on conventional
laminates, failure is mainly within the pad cratering on board assemblies. Part of
and lead-free for customers. He will be running
laminate to copper interface, and the trend the issue is also due to the rigidity of the
four workshops in South Africa during May,
appears to be a progressive degradation of tin/silver/copper alloys, high strength but
details are available from SMART Group South
the mechanical properties of the laminate lower ductility.
Africa at www.smartgroupsa.org Bob sets up
after successive reflow operations. The Details of the SMART Group and its
and optimises production lines for users and also
FR4 samples show a slight increase of the activities can be found at www.smartgroup.org.
provides conferences and workshops worldwide.
shear strength of the solder after successive
reflow operations.
For further information on workshops at ITRI
in Europe, training materials, lead-free and on-
line process support visit www.ASKbobwillis.com
Figure 6. Results of shear testing after two additional reflow operations on the
panels. The results on the FR4 vary after three reflow cycles, but the results are still
higher than the lead-free laminates.
www.globalsmt.net Global SMT & Packaging – May 2009 – 5
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