Editing Ball grid array (section)

== Disadvantages ==
[[Image:BGA joint xray.jpg|thumb|120px|[[X-ray]] of BGA]]

=== Lack of compliance===
A disadvantage of BGAs is that the solder balls cannot flex in the way that longer leads can, so they are not mechanically [[stiffness#Compliance|compliant]]. As with all surface mount devices, bending due to a difference in [[Thermal expansion|coefficient of thermal expansion]] between PCB substrate and BGA (thermal stress) or flexing and vibration (mechanical stress) can cause the solder joints to fracture.

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 |access-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.

Another solution to non-compliant connections is to put a "compliant layer" in the package that allows the balls to physically move in relation to the package.  This technique has become standard for packaging DRAMs in BGA packages.

Other techniques for increasing the board-level reliability of packages include use of low-expansion PCBs for ceramic BGA (CBGA) packages, [[interposer]]s between the package and PCB, and re-packaging a device.<ref name=underfill/>

===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=Industrial Computed Tomography Scanning Services – JG&A |access-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.

A cheaper and easier inspection method, albeit destructive, is becoming increasingly popular because it does not require special equipment. Commonly referred to as [[Dye-and-Pry|dye and pry]], the process includes immersing the entire PCB or just the BGA attached module into a [[dye]], and after drying, the module is pried off and the broken joins are inspected. If a solder location contains the dye, then it indicates that the connection was imperfect.<ref>{{cite web
 | url = http://www.cascade-eng.com/docs/CS_FA_01.pdf
 | title = Dye and Pry of BGA Solder Joints
 | date = 2013-11-22
 | access-date = 2014-03-22
 | publisher = cascade-eng.com
 | archive-url = https://web.archive.org/web/20111016215109/http://www.cascade-eng.com/CESResourceLib/CS_FA_01.pdf
 | archive-date = 2011-10-16
 |url-status = dead
 }}</ref>

=== Difficulties during circuit development ===
During development it is not practical to solder BGAs into place, and sockets are used instead, but tend to be unreliable. There are two common types of socket: the more reliable type has spring pins that push up under the balls, although it does not allow using BGAs with the balls removed as the spring pins may be too short.

The less reliable type is a [[ZIF socket]], with spring pinchers that grab the balls. This does not work well, especially if the balls are small.{{Citation needed|date=March 2013}}

=== Cost of equipment ===
Expensive equipment is required to reliably solder BGA packages; hand-soldering BGA packages is very difficult and unreliable, usable only for the smallest packages in the smallest quantities.<ref>{{cite news |last=Das |first=Santosh |url=http://www.electronicsandyou.com/blog/bga-ball-grid-array-repairing-and-soldering-bga.html |title=BGA Soldering & Repairing / How to Solder Ball Grid Array |work=Electronics and You |date=2019-08-22 |accessdate=2021-09-07 }}</ref> However, as more ICs have become available only in leadless (e.g. [[quad-flat no-leads package]]) or BGA packages, various DIY [[Rework (electronics)#Reflowing and reballing|reflow]] methods have been developed using inexpensive heat sources such as [[heat gun]]s, and domestic [[Toaster#Toaster oven|toaster ovens]] and [[Frying pan#Electric|electric skillets]].<ref>[https://www.sparkfun.com/tutorials/59 Sparkfun tutorials: Reflow skillet, July 2006]</ref>