HOME

TheInfoList



OR:

A ball grid array (BGA) is a type of surface-mount packaging (a chip carrier) used for integrated circuits. BGA packages are used to permanently mount devices such as
microprocessor A microprocessor is a computer processor where the data processing logic and control is included on a single integrated circuit, or a small number of integrated circuits. The microprocessor contains the arithmetic, logic, and control circ ...
s. A BGA can provide more interconnection pins than can be put on a dual in-line or flat package. The whole bottom surface of the device can be used, instead of just the perimeter. The traces connecting the package's leads to the wires or balls which connect the die to package are also on average shorter than with a perimeter-only type, leading to better performance at high speeds. BGAs were introduced in the 1990s and became popular by 2001. Soldering of BGA devices requires precise control and is usually done by automated processes such as in computer-controlled automatic
reflow oven A reflow oven is a machine used primarily for reflow soldering of surface mount electronic components to printed circuit boards (PCBs). In commercial high-volume use, reflow ovens take the form of a long tunnel containing a conveyor belt along wh ...
s.


Description

The BGA is descended from the pin grid array (PGA), which is a package with one face covered (or partly covered) with pins in a grid pattern which, in operation, conduct electrical signals between the integrated circuit and the printed circuit board (PCB) on which it is placed. In a BGA the pins are replaced by pads on the bottom of the package, each initially with a tiny solder ball stuck to it. These solder spheres can be placed manually or by automated equipment, and are held in place with a tacky flux. The device is placed on a PCB with copper pads in a pattern that matches the solder balls. The assembly is then heated, either in a
reflow oven A reflow oven is a machine used primarily for reflow soldering of surface mount electronic components to printed circuit boards (PCBs). In commercial high-volume use, reflow ovens take the form of a long tunnel containing a conveyor belt along wh ...
or by an
infrared heater An infrared heater or heat lamp is a body with a higher temperature which transfers energy to a body with a lower temperature through electromagnetic radiation. Depending on the temperature of the emitting body, the wavelength of the peak of the i ...
, melting the balls. Surface tension causes the molten solder to hold the package in alignment with the circuit board, at the correct separation distance, while the solder cools and solidifies, forming soldered connections between the device and the PCB. In more advanced technologies, solder balls may be used on both the PCB and the package. Also, in stacked
multi-chip module A multi-chip module (MCM) is generically an electronic assembly (such as a package with a number of conductor terminals or "pins") where multiple integrated circuits (ICs or "chips"), semiconductor dies and/or other discrete components are in ...
s, (
package on package Package on a package (PoP) is an integrated circuit packaging method to vertically combine discrete logic and memory ball grid array (BGA) packages. Two or more packages are installed atop each other, i.e. stacked, with a standard interface to rout ...
) solder balls are used to connect two packages.


Advantages


High density

The BGA is a solution to the problem of producing a miniature package for an integrated circuit with many hundreds of pins. Pin grid arrays and dual-in-line surface mount ( SOIC) packages were being produced with more and more pins, and with decreasing spacing between the pins, but this was causing difficulties for the soldering process. As package pins got closer together, the danger of accidentally bridging adjacent pins with solder grew.


Heat conduction

A further advantage of BGA packages over packages with discrete leads (i.e. packages with legs) is the lower
thermal resistance Thermal resistance is a heat property and a measurement of a temperature difference by which an object or material resists a heat flow. Thermal resistance is the reciprocal of thermal conductance. * (Absolute) thermal resistance ''R'' in kelvi ...
between the package and the PCB. This allows heat generated by the integrated circuit inside the package to flow more easily to the PCB, preventing the chip from overheating.


Low-inductance leads

The shorter an electrical conductor, the lower its unwanted inductance, a property which causes unwanted distortion of signals in high-speed electronic circuits. BGAs, with their very short distance between the package and the PCB, have low lead inductances, giving them superior electrical performance to pinned devices.


Disadvantages


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 compliant. As with all surface mount devices, bending due to a difference in
coefficient of thermal expansion Thermal expansion is the tendency of matter to change its shape, area, volume, and density in response to a change in temperature, usually not including phase transitions. Temperature is a monotonic function of the average molecular kineti ...
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 The Restriction of Hazardous Substances Directive 2002/95/EC (RoHS 1), short for Directive on the restriction of the use of certain hazardous substances in electrical and electronic equipment, was adopted in February 2003 by the European Unio ...
lead-free solder alloy assemblies has presented some further challenges to BGAs including " head in pillow" soldering phenomenon, "
pad cratering Pad cratering is a mechanically induced fracture in the resin between copper foil and outermost layer of fiberglass of a printed circuit board (PCB). It may be within the resin or at the resin to fiberglass interface. The pad remains connected to t ...
" 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. Mechanical stress issues can be overcome by bonding the devices to the board through a process called "underfilling",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
tin whisker Metal whiskering is a phenomenon which occurs in electrical devices when metals form long whisker-like projections over time. Tin whiskers were noticed and documented in the vacuum tube era of electronics early in the 20th century in equipment t ...
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, interposers between the package and PCB, and re-packaging a device.


Difficulty of inspection

Once the package is soldered into place, it is difficult to find soldering faults.
X-ray An X-ray, or, much less commonly, X-radiation, is a penetrating form of high-energy electromagnetic radiation. Most X-rays have a wavelength ranging from 10  picometers to 10  nanometers, corresponding to frequencies in the range 30&nb ...
machines,
industrial CT scanning Industrial computed tomography (CT) scanning is any computer-aided tomographic process, usually X-ray computed tomography, that uses irradiation to produce three-dimensional internal and external representations of a scanned object. Industrial CT ...
machines, 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 A thermocouple, also known as a "thermoelectrical thermometer", is an electrical device consisting of two dissimilar electrical conductors forming an electrical junction. A thermocouple produces a temperature-dependent voltage as a result of th ...
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, 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.


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 Zero insertion force (ZIF) is a type of IC socket or electrical connector that requires very little (but not literally zero) force for insertion. With a ZIF socket, before the IC is inserted, a lever or slider on the side of the socket is move ...
, with spring pinchers that grab the balls. This does not work well, especially if the balls are small.


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. However, as more ICs have become available only in leadless (e.g. quad-flat no-leads package) or BGA packages, various DIY
reflow Reflow soldering is a process in which a solder paste (a sticky mixture of powdered solder and flux) is used to temporarily attach one or thousands of tiny electrical components to their contact pads, after which the entire assembly is subject ...
methods have been developed using inexpensive heat sources such as
heat gun A heat gun is a device used to emit a stream of hot air, usually at temperatures between 100 °C and 550 °C (200-1000 °F), with some hotter models running around 760 °C (1400 °F), which can be held by hand. Heat ...
s, and domestic toaster ovens and electric skillets.


Variants

* ''CABGA'': chip array ball grid array * ''CBGA'' and ''PBGA'' denote the ''c''eramic or ''p''lastic substrate material to which the array is attached. * ''CTBGA'': thin chip array ball grid array * ''CVBGA'': very thin chip array ball grid array * ''DSBGA'': die-size ball grid array * ''FBGA'': fine ball grid array based on ''ball grid array'' technology. It has thinner contacts and is mainly used in
system-on-a-chip A system on a chip or system-on-chip (SoC ; pl. ''SoCs'' ) is an integrated circuit that integrates most or all components of a computer or other electronic system. These components almost always include a central processing unit (CPU), memory ...
designs;
also known as ''fine pitch ball grid array'' (
JEDEC The JEDEC Solid State Technology Association is an independent semiconductor engineering trade organization and standardization body headquartered in Arlington County, Virginia, United States. JEDEC has over 300 members, including some of the w ...
-Standard) or
''fine line BGA'' by
Altera Altera Corporation was a manufacturer of programmable logic devices (PLDs) headquartered in San Jose, California. It was founded in 1983 and acquired by Intel in 2015. The main product lines from Altera were the flagship Stratix series, mid-ran ...
. Not to be confused with ''fortified BGA.'' * ''FCmBGA'': flip chip molded ball grid array * ''LBGA'': low-profile ball grid array * ''LFBGA'': low-profile fine-pitch ball grid array * ''MBGA'': micro ball grid array * ''MCM-PBGA'': multi-chip module plastic ball grid array * ''nFBGA'': New Fine Ball Grid Array * ''PBGA'': plastic ball grid array * ''SuperBGA (SBGA)'': super ball grid array * ''TABGA'': tape array BGA * ''TBGA'': thin BGA * ''TEPBGA'': thermally enhanced plastic ball grid array * ''TFBGA'' or thin and fine ball grid array * ''UFBGA'' and ''UBGA'' and ultra fine ball grid array based on pitch ball grid array. * ''VFBGA'': very fine pitch ball grid array * ''WFBGA'': very very thin profile fine pitch ball grid array Effectively also the
flip chip Flip chip, also known as controlled collapse chip connection or its abbreviation, C4, is a method for interconnecting dies such as semiconductor devices, IC chips, integrated passive devices and microelectromechanical systems (MEMS), to exter ...
methods for mounting chip dies to a carrier is sort of a BGA design derivate with the functional equivalent of the balls there being called bumps or micro bumps. This is realized at an already microscopic size level. To make it easier to use ball grid array devices, most BGA packages only have balls in the outer rings of the package, leaving the innermost square empty. Intel used a package designated BGA1 for their
Pentium II The Pentium II brand refers to Intel's sixth-generation microarchitecture (" P6") and x86-compatible microprocessors introduced on May 7, 1997. Containing 7.5 million transistors (27.4 million in the case of the mobile Dixon with 256  KB ...
and early
Celeron Celeron is Intel's brand name for low-end IA-32 and x86-64 computer microprocessor models targeted at low-cost personal computers. Celeron processors are compatible with IA-32 software. They typically offer less performance per clock speed com ...
mobile processors. BGA2 is Intel's package for their
Pentium III The Pentium III (marketed as Intel Pentium III Processor, informally PIII or P3) brand refers to Intel's 32-bit x86 desktop and mobile CPUs based on the sixth-generation P6 microarchitecture introduced on February 28, 1999. The brand's initial ...
and some later Celeron mobile processors. BGA2 is also known as FCBGA-479. It replaced its predecessor, BGA1. For example, the "micro-FCBGA" (flip chip ball grid array) is Intel's current BGA mounting method for mobile processors that use a
flip chip Flip chip, also known as controlled collapse chip connection or its abbreviation, C4, is a method for interconnecting dies such as semiconductor devices, IC chips, integrated passive devices and microelectromechanical systems (MEMS), to exter ...
binding technology. It was introduced with the ''Coppermine'' Mobile Celeron. Micro-FCBGA has 479 balls that are 0.78 mm in diameter. The processor is affixed to the motherboard by soldering the balls to the motherboard. This is thinner than a pin grid array socket arrangement, but is not removable. The 479 balls of the Micro-FCBGA package (a package almost identical to the 478-pin socketable micro-FCPGA package) are arranged as the 6 outer rings of a 1.27 mm pitch (20 balls per inch pitch) 26x26 square grid, with the inner 14x14 region empty.


Procurement

Primary end-users of BGAs are
original equipment manufacturer An original equipment manufacturer (OEM) is generally perceived as a company that produces non-aftermarket parts and equipment that may be marketed by another manufacturer. It is a common industry term recognized and used by many professional or ...
s (OEMs). There is also a market among electronic hobbyists do it yourself (DIY) such as the increasingly popular
maker movement The maker culture is a contemporary subculture representing a technology-based extension of DIY culture that intersects with hardware-oriented parts of hacker culture and revels in the creation of new devices as well as tinkering with existing on ...
. While OEMs generally source their components from the manufacturer, or the manufacturer's distributor, the hobbyist will typically obtain BGAs on the aftermarket through electronic component brokers or
distributors A distributor is an enclosed rotating switch used in spark-ignition internal combustion engines that have mechanically timed ignition. The distributor's main function is to route high voltage current from the ignition coil to the spark plugs ...
.


See also

* Dual in-line package (DIP) * Pin grid array (PGA) *
Land grid array The land grid array (LGA) is a type of surface-mount packaging for integrated circuits (ICs) that is notable for having the pins on the socket (when a socket is used) rather than the integrated circuit. An LGA can be electrically connected to a ...
(LGA) * Thin quad flat pack (TQFP) *
Small-outline integrated circuit A small outline integrated circuit (SOIC) is a surface-mounted integrated circuit (IC) package which occupies an area about 30–50% less than an equivalent dual in-line package (DIP), with a typical thickness being 70% less. They are general ...
(SOIC) * Chip carrier: chip packaging and package types list * Embedded wafer level ball grid array


References


External links


PBGA Package Information
from
Amkor Technology Amkor Technology, Inc. is a semiconductor product packaging and test services provider. The company has been headquartered in Tempe, Arizona, since 2005, when it was moved from West Chester, Pennsylvania. The company was founded in 1968 and, , ha ...

PBGA Package Information
from J-Devices Corporation {{Semiconductor packages Chip carriers