Ball grid array: Difference between revisions

Revision as of 19:54, 28 December 2020

Revision as of 08:21, 30 December 2020

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Thermal expansion issues can be overcome by matching the mechanical and thermal characteristics of the PCB to those of the package. Typically, plastic BGA devices more closely match PCB thermal characteristics than ceramic devices.

The predominant use of [[RoHS compliant]] lead-free solder alloy assemblies has presented some further challenges to BGAs including "[[Head in pillow (metallurgy)|head in pillow]]"<ref>{{cite web |title=Reducing Head in Pillow Defects - Head in pillow defects: causes and potential solutions |author=Alpha |date=2010-03-15 |orig-year=September 2009 |version=3 |url=http://www.slideshare.net/Alpha1Cookson/head-on-pillow-v3-sept-09 |access-date=2018-06-18 |url-status = live|archive-url=https://web.archive.org/web/20131203002809/http://www.slideshare.net/Alpha1Cookson/head-on-pillow-v3-sept-09 |archive-date=2013-12-03}}</ref> soldering phenomenon, "[[pad cratering]]" problems as well as their decreased reliability versus lead-based solder BGAs in extreme operating conditions such as high temperature, high thermal shock and high gravitational force environments, in part due to lower ductility of RoHS-compliant solders.<ref>{{cite web |url=http://teerm.nasa.gov/NASA_DODLeadFreeElectronics_Proj2.htm |title=TEERM - TEERM Active Project - NASA-DOD Lead-Free Electronics (Project 2) |publisher=Teerm.nasa.gov |accessdateaccess-date=2014-03-21 |archive-url=https://web.archive.org/web/20141008003914/http://teerm.nasa.gov/nasa_dodleadfreeelectronics_proj2.htm |archive-date=2014-10-08 |url-status = dead}}</ref>

Mechanical stress issues can be overcome by bonding the devices to the board through a process called "underfilling",<ref name=underfill>[https://archive.today/20130719180947/http://www.electroiq.com/articles/ap/print/volume-10/issue-12/features/bga-underfills.html Solid State Technology: BGA underfills - Increasing board-level solder joint reliability, 12/01/2001]</ref> which injects an epoxy mixture under the device after it is soldered to the PCB, effectively gluing the BGA device to the PCB. There are several types of underfill materials in use with differing properties relative to workability and thermal transfer. An additional advantage of underfill is that it limits [[Whisker (metallurgy)|tin whisker]] growth.

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===Difficulty of inspection===

Once the package is soldered into place, it is difficult to find soldering faults. [[X-ray]] machines, [[industrial CT scanning]] machines,<ref>"CT Services - Overview." Jesse Garant & Associates. August 17, 2010. {{cite web|url=http://www.jgarantmc.com/ct-services.html |title=Archived copy |accessdateaccess-date=2010-11-24 |url-status = dead|archive-url=https://web.archive.org/web/20100923150138/http://www.jgarantmc.com/ct-services.html |archive-date=2010-09-23 }}</ref> special microscopes, and endoscopes to look underneath the soldered package have been developed to overcome this problem. If a BGA is found to be badly soldered, it can be removed in a ''[[rework station]]'', which is a jig fitted with infrared lamp (or hot air), a [[thermocouple]] and a vacuum device for lifting the package. The BGA can be replaced with a new one, or it can be refurbished (or ''reballed'') and re-installed on the circuit board. Pre-configured solder balls matching the array pattern can be used to reball BGAs when only one or a few need to be reworked. For higher volume and repeated lab work, a stencil-configured vacuum-head pick-up and placement of loose spheres can be used.

Due to the cost of visual X-ray BGA inspection, electrical testing is very often used instead. Very common is [[boundary scan]] testing using an IEEE 1149.1 [[JTAG]] port.

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| title = Dye and Pry of BGA Solder Joints

| date = 2013-11-22

| accessdateaccess-date = 2014-03-22

| publisher = cascade-eng.com

| format = PDF