September, 2017


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Ambient Shadow Moiré Warpage Measurements Reduce Defect Rates


Continued from previous page


array and removing excess copper, warpage was reduced significantly and the target yield of 1,500 DPM was achieved.


Challenging New Materials


It is easy to imagine that many defects, such as head-in-pillow, cold solder, bridging, etc., could be avoided if challenging PCBs and logic devices were measured for coplanarity before assembly. The shadow moiré method used in this study allowed the team to collect up to 1.4 million data points in less than two seconds with a z-resolution accuracy of 1.25 μm. The researchers were able to capture a wealth of data by measuring each board, without impacting the cycle rate of the assembly line. And, the team was able to give each board a traceable identity, so that all of the data for each PCB was saved in graphical, tabular, and 3D formats.


Warpage issues seem to occur primarily in two different areas. Small, dense and lightweight assem- blies for mobile and medical indus- tries are more sensitive to CTE vari- ation in materials and components. On the other hand, large, thick and bulky assemblies for telecommunica- tions and computing are being


X-ray Shows the Best and Worst of BGA Assembly


Continued from page 73


Missing Balls. Missing solder balls are often easy to identify using a good X-ray machine. The pad can be seen, but the dark circle of the solder ball will not be there. This problem has a few different causes.


The first is mechanical, if some- one or something hit the solder ball and caused it to fall from the pack- age. The second is metallurgical, which causes the solder not to wet to the pad.


Another possible cause is the stencil used to print the solder balls. A dirty stencil with a clogged opening will not deposit enough solder on the pad to create a ball. The density of the solder paste must also be investi- gated, since a thick solder may not be able to properly flow through the stencil.


Even with all the possible defects, the industry has seen a dra- matic improvement in yield going from fine-pitch leaded parts to BGAs. When we also take into consideration the overall simplification of the man- ufacturing process that came with the BGA revolution, it’s safe to say that BGAs are here to stay. Contact: Creative Electron, Inc., 253 Pawnee Street, San Marcos, CA 92078  760-752-1192 fax: 760-752-1196


E-mail: info@creativeelectron.com Web: www.creativeelectron.com 


Additional authors who con- tributed to this article include Dr. Glen Thomas, Griffin Lemaster, Christopher Jimenez, David Phillips, Carlos Valenzuela, Mariem Ortiz, and Brian Wagner of Creative Electron.


FlexLink is part of Coesia, a group of innovation-based industrial solutions companies operating globally headquartered in Bologna, Italy. www.coesia.com


required to have greater performance with the same footprint.


Lifted corner exceeds seating plane of 0.18 mm (0.007 in.), resulting in a much higher probability of a solder joint defect underneath.


Both of these trends produce their own anom- alies, which make the components and assemblies susceptible to warpage-related defects. But, meas- uring the boards, materials and components for both verification and analysis prior to final assem- bly is an excellent strategy to get as close as possi- ble to zero defects. Contact: Akrometrix LLC, 2700 NE Expressway, Building B, Suite 500, Atlanta, GA 30345  404-486-0880 E-mail: emoen@akrometrix.com Web: www.akrometrix.com 


See at SMTAI, Booth 124


Page 75


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See at SMTAI, Booth 407


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