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January 21, 2008
BGA bridging defects
How do you find the root cause of BGA bridging?
We are seeing two different bridging areas: one is in the corner and the other is in the centre of the array?
Is there a way to fine tune the profile to eliminate these defects?
Peter Gog
Huawei Tech
This "Ask the Experts" page has been viewed 693 times.
Ask the Experts Comments
January 21, 2008
Sure, blame it on the reflow oven and profile - because that's where the bridges happened, right? In reality, you might want to check out the solder paste.
First of all, make sure that the profile you are using conforms to what the solder paste manufacturer specifies - you may be suffering from "hot slump".
Also, be sure you have the correct solder paste deposit height - yours might be excessive. Anyone assembling with area arrays should have 3-D post-print inspection, at least on an AQL basis. If these actions fail, it might be time to evaluate a new solder paste.
Phil Zarrow, Principal Consultant
ITM Consulting
phil_zarrow@ITMconsulting.org
 Mr. Zarrow has been involved with PCB assembly for more than thirty years. His expertise includes the manufacture of equipment for circuit board fabrication and assembly of through-hole and surface mount technologies. In addition to his background in automated assembly and reflow soldering, Mr. Zarrow is recognized for his expertise in troubleshooting SMT manufacturing and lead-free implementation. He has extensive hands-on experience with set-up and troubleshooting through-hole and SMT processes throughout the world.
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January 21, 2008
Typical causes of the bridging you describe is excessive top side reflow temperatures. I would suggest you reduce you top-side temperature and increase the subzone temperature. This will reduce the thermal stresses on the component and reduce the chances of the component warping.
Edward Zamborsky, Regional Sales Manager
OK International Inc.
 Mr. Zamborsky serves as one of OK's technology advisors to the Product Development group. Ed has authored many articles, and has presented many papers on topics such as; Low Volume SMT Assembly, Solder Fume Extraction, SMT Rework, BGA Rework, Lead Free Hand Soldering, Lead Free Visual Inspection and Lead Free Array Rework.
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January 21, 2008
My initial thoughts are that you are getting warpage or possible popcorning of the packages. Have moisture sensitivity protocols been followed for the BGAs?
Dr. David Bernard, Product Manager
Dage Precision Industries
d.bernard@dage-group.com
 Mr. Bernard has been the X-ray Systems Product Manager at Dage for over 5 years and have been involved in all aspects of x-ray inspection and test for printed circuit board assembly applications. Prior to this, Dr. bernard was working with radiation measurement instrumentation.
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January 21, 2008
Take a methodical approach. First, look at the board bond pads. Board shops often (too often) make changes in the design and do not communicate this to the end customer. Ensure that the spacing between bond pads is uniform throughout under the BGA
Next, take a look at the BGA. Is the spacing between the balls uniform? Deliberate changes (such as an array that is not fully populated) or unintended changes could drive this behavior.
Finally, do the same thing with your stencil pattern.
If everything looks good, then I would start to suspect out of plane deformation of the BGA (aka, potato chipping) during the reflow process.
Dr. Craig D. Hillman, CEO & Managing Partner
DfR Solutions
chillman@dfrsolutions.com
 Dr. Hillman's specialties include best practices in Design for Reliability, strategies for transitioning to Pb-free, supplier qualification (commodity and engineered products), passive component technology and printed board failure mechanisms. Dr. Hillman has over 30 publications and has presented on a wide variety of reliability issues to over 150 companies and organizations.
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