We have a BGA component that is shifting during inline reflow. The BGA is shifting enough to cause some open joints.
The BGA component is a full array with 400 balls and 1mm pitch. We are using a standard tin-lead reflow process.
The component shift is definitely happening during reflow as we have checked the position prior to reflow using our X-ray system.
What could likely be the cause of the BGA shifting?
I. G.
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Ask the Experts Comments
Before mentioning any comments, what is the reflow configuration, paste which you are using and also the location of BGA in the PCB i.e in the center or on the PCB edge?
Sandip Thakor has 9 years of experience in electronics industry specializing in soldering technology. Thakor has experience in lead free installation, process optimization and developing quality standards.
I would check the level of the oven, and the velocity of the convection fans.
Before I got too crazy, I would rotate the PCB 180° and see if that helps.
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 articles and 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.
This is an interesting problem because BGA devices are supposed to self center when the solder melts.
If the board is warping at temperature or the rails of the oven are not flat, would be a place to start looking.
I would also look at how long the board is at temperature for. Perhaps a longer or shorter time would work.
If all else fails you could always lock down the corner of the device with a surface mount adhesive.
Steven Adamson is Market Manager for Asymtek. He has worked for Kodak, Motorola and Plessey, ICL in the UK. He holds five US and 2 UK patents, was awarded a HNC in electrical engineering and was 2008 President of IMAPS.
Without seeing the board, the types of components being loaded, board finish, and the paste type being used, the following are possible causes:
Excessive surface tension under the part could be the cause. To address this, try reducing the volume of paste the stencil is depositing by either reducing the stencil thickness, or reducing the size and or shape of the aperture.
Oven profile could also be a factor. Check to be sure the zones are uniform. Inconsistent heating zones could be causing the shifting.
Finally, large ground planes or larger components on the board could be acting as a heat sink or heat shield, could be contributing to the problem.
Stephanie Henninger is the Director of Technical Services & Marketing for Integrated Ideas & Technologies, Inc., a premier manufacturer of SMT stencils. She has been instrumental in the stencil design and technical support.
Movement of a component could be caused by elevated mechanical vibrations stemming from a questionable conveyor system or blower motor.
Other sub-systems to explore would be sources of impinging gas, such as outputs of convection plenums, cooling tubes, recirculation returns or gas distribution plumbing in both the heating or cooling regions of the reflow system.
Uneven heating or especially cooling can cause dissimilar forces that can shift a component, this is frequently witnessed with passives but larger devices are not immune from this phenomenon.
A quick test to eliminate the heating & cooling variables would be to duplicate the process with a few identical samples processed through the reflow system while set-up to operate at room temperature.
If the component continued to shift, chances are its oven related. If it didn’t move, then it may be thermal related such as device uniformity, heating rates and cooling rates. I’d also double check pad-package geometries to be safe
Mr. Cabral has been involved with advanced manufacturing and new product introduction, along with process and product development within the electronics industry for 25 years. He is widely recognized as a major contributor to the development and optimization of thermal systems.
Reader Comments
BGA devices are supposed to self center when they reflow. It may be possible that the BGA is ROHS and your process uses standard tin-lead. The solder paste will reflow before the BGA solder balls and this timing mismatch may create the shift.
