Ball grid array

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A grid array of solder balls under an integrated circuit chip, with the chip removed; the balls were left attached to the printed circuit board. Solder ball grid.jpg
A grid array of solder balls under an integrated circuit chip, with the chip removed; the balls were left attached to the printed circuit board.

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 microprocessors. 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.

Chip carrier one of several kinds of surface mount technology packages for integrated circuits

In electronics, a chip carrier is one of several kinds of surface-mount technology packages for integrated circuits. Connections are made on all four edges of a square package; Compared to the internal cavity for mounting the integrated circuit, the package overall size is large.

Integrated circuit electronic circuit manufactured by lithography; set of electronic circuits on one small flat piece (or "chip") of semiconductor material, normally silicon 639-1 ısoo

An integrated circuit or monolithic integrated circuit is a set of electronic circuits on one small flat piece of semiconductor material that is normally silicon. The integration of large numbers of tiny transistors into a small chip results in circuits that are orders of magnitude smaller, cheaper, and faster than those constructed of discrete electronic components. The IC's mass production capability, reliability and building-block approach to circuit design has ensured the rapid adoption of standardized ICs in place of designs using discrete transistors. ICs are now used in virtually all electronic equipment and have revolutionized the world of electronics. Computers, mobile phones, and other digital home appliances are now inextricable parts of the structure of modern societies, made possible by the small size and low cost of ICs.

Microprocessor computer processor contained on an integrated-circuit chip

A microprocessor is a computer processor that incorporates the functions of a central processing unit on a single integrated circuit (IC), or at most a few integrated circuits. The microprocessor is a multipurpose, clock driven, register based, digital integrated circuit that accepts binary data as input, processes it according to instructions stored in its memory, and provides results as output. Microprocessors contain both combinational logic and sequential digital logic. Microprocessors operate on numbers and symbols represented in the binary number system.

Contents

Soldering of BGA devices requires precise control and is usually done by automated processes.

Description

BGA ICs assembled on a RAM stick BGA RAM.jpg
BGA ICs assembled on a RAM stick

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. [1] 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 or by an infrared heater, 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.

Pin grid array type of integrated circuit packaging. In a PGA, the package is square or rectangular, and the pins are arranged in a regular array on the underside of the package

A pin grid array, often abbreviated PGA, is a type of integrated circuit packaging. In a PGA, the package is square or rectangular, and the pins are arranged in a regular array on the underside of the package. The pins are commonly spaced 2.54 mm (0.1") apart, and may or may not cover the entire underside of the package.

Printed circuit board board to support and connect electronic components

A printed circuit board (PCB) mechanically supports and electrically connects electronic components or electrical components using conductive tracks, pads and other features etched from one or more sheet layers of copper laminated onto and/or between sheet layers of a non-conductive substrate. Components are generally soldered onto the PCB to both electrically connect and mechanically fasten them to it.

Solder ball

In integrated circuit packaging, a solder ball, also a solder bump is a ball of solder that provides the contact between the chip package and the printed circuit board, as well as between stacked packages in multichip modules. The solder balls can be placed manually or by automated equipment, and are held in place with a tacky flux.

In more advanced technologies, solder balls may be used on both the PCB and the package. Also, in stacked multi-chip modules, solder balls are used to connect two packages.

Multi-chip module

A multi-chip module (MCM) is generically an electronic assembly where multiple integrated circuits, semiconductor dies and/or other discrete components are integrated, usually onto a unifying substrate, so that in use it is treated as if it were a single component . Other terms, such as "hybrid" or "hybrid integrated circuit", also refer to MCMs.

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 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.

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.

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.

Inductance electrical property


In electromagnetism and electronics, inductance describes the tendency of an electrical conductor, such as coil, to oppose a change in the electric current through it. The change in current induces a reverse electromotive force (voltage). When an electric current flows through a conductor, it creates a magnetic field around that conductor. A changing current, in turn, creates a changing magnetic field, the surface integral of which is known as magnetic flux. From Faraday's law of induction, any change in magnetic flux through a circuit induces an electromotive force (voltage) across that circuit, a phenomenon known as electromagnetic induction. Inductance is specifically defined as the ratio between this induced voltage and the rate of change of the current in the circuit

Disadvantages

X-ray of BGA BGA joint xray.jpg
X-ray of BGA

Noncompliant connections

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 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" [2] 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. [3]

Mechanical stress issues can be overcome by bonding the devices to the board through a process called "underfilling", [4] 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 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. [4]

Difficulty of inspection

Once the package is soldered into place, it is difficult to find soldering faults. X-ray machines, industrial CT scanning machines, [5] 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.

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. [6]

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 ]

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.[ citation needed ] However, as more ICs have become available only in leadless (e.g. quad-flat no-leads package) or BGA packages, various DIY reflow methods have been developed using inexpensive heat sources such as heat guns, and domestic toaster ovens and electric skillets. [7]

Variants

Intel Mobile Celeron in a BGA2 package (FCBGA-479); the die is blue Celeron mobile.jpg
Intel Mobile Celeron in a BGA2 package (FCBGA-479); the die is blue

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 and early Celeron mobile processors. BGA2 is Intel's package for their Pentium III 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[ when? ] BGA mounting method for mobile processors that use a flip chip binding technology. It was introduced with the Coppermine Mobile Celeron.[ citation needed ] 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. [10] [11]

Procurement

Primary end-users of BGAs are original equipment manufacturers (OEMs). There is also a market among electronic hobbyists do it yourself (DIY) such as the increasingly popular maker movement. [12] 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.

See also

Related Research Articles

Dual in-line package

In microelectronics, a dual in-line package, or dual in-line pin package (DIPP) is an electronic component package with a rectangular housing and two parallel rows of electrical connecting pins. The package may be through-hole mounted to a printed circuit board (PCB) or inserted in a socket. The dual-inline format was invented by Don Forbes, Rex Rice and Bryant Rogers at Fairchild R&D in 1964, when the restricted number of leads available on circular transistor-style packages became a limitation in the use of integrated circuits. Increasingly complex circuits required more signal and power supply leads ; eventually microprocessors and similar complex devices required more leads than could be put on a DIP package, leading to development of higher-density packages. Furthermore, square and rectangular packages made it easier to route printed-circuit traces beneath the packages.

Surface-mount technology method for producing electronic circuits

Surface-mount technology (SMT) is a method for producing electronic circuits in which the components are mounted or placed directly onto the surface of printed circuit boards (PCBs). An electronic device so made is called a surface-mount device (SMD). In industry, it has largely replaced the through-hole technology construction method of fitting components with wire leads into holes in the circuit board. Both technologies can be used on the same board, with the through-hole technology used for components not suitable for surface mounting such as large transformers and heat-sinked power semiconductors.

Flip chip, also known as controlled collapse chip connection or its abbreviation, C4, is a method for interconnecting semiconductor devices, such as IC chips and microelectromechanical systems (MEMS), to external circuitry with solder bumps that have been deposited onto the chip pads. The technique was developed by General Electric's Light Military Electronics Dept., Utica, N.Y. The solder bumps are deposited on the chip pads on the top side of the wafer during the final wafer processing step. In order to mount the chip to external circuitry, it is flipped over so that its top side faces down, and aligned so that its pads align with matching pads on the external circuit, and then the solder is reflowed to complete the interconnect. This is in contrast to wire bonding, in which the chip is mounted upright and wires are used to interconnect the chip pads to external circuitry.

Integrated circuit packaging Final stage of semiconductor device fabrication

In electronics manufacturing, integrated circuit packaging is the final stage of semiconductor device fabrication, in which the block of semiconductor material is encapsulated in a supporting case that prevents physical damage and corrosion. The case, known as a "package", supports the electrical contacts which connect the device to a circuit board.

CPU socket provides mechanical and electrical connections between a microprocessor and a printed circuit board

In computer hardware, a CPU socket or CPU slot comprises one or more mechanical components providing mechanical and electrical connections between a microprocessor and a printed circuit board (PCB). This allows for placing and replacing the central processing unit (CPU) without soldering.

Land grid array type of surface-mount packaging for integrated circuits

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 rather than the integrated circuit. An LGA can be electrically connected to a printed circuit board (PCB) either by the use of a socket or by soldering directly to the board.

Quad Flat Package surface mount integrated circuit package

A QFP or Quad Flat Package is a surface-mounted integrated circuit package with "gull wing" leads extending from each of the four sides. Socketing such packages is rare and through-hole mounting is not possible. Versions ranging from 32 to 304 pins with a pitch ranging from 0.4 to 1.0 mm are common. Other special variants include low-profile QFP (LQFP) and thin QFP (TQFP).

Reflow soldering

Reflow soldering is a process in which a solder paste is used to temporarily attach one or thousands of tiny electrical components to their contact pads, after which the entire assembly is subjected to controlled heat. The solder paste reflows in a molten state, creating permanent solder joints. Heating may be accomplished by passing the assembly through a reflow oven or under an infrared lamp or by soldering individual joints [unconventionally] with a desoldering hot air pencil.

Rework (electronics) term for the refinishing operation or repair of an electronic printed circuit board (PCB) assembly

Rework is the term for the refinishing operation or repair of an electronic printed circuit board (PCB) assembly, usually involving desoldering and re-soldering of surface-mounted electronic components (SMD). Mass processing techniques are not applicable to single device repair or replacement, and specialized manual techniques by expert personnel using appropriate equipment are required to replace defective components; area array packages such as ball grid array (BGA) devices particularly require expertise and appropriate tools. A hot air gun or hot air station is used to heat devices and melt solder, and specialised tools are used to pick up and position often tiny components.

Socket 479

Socket 479 (mPGA479M) is the CPU socket for the Intel Pentium M and Celeron M, mobile processors. Normally used in laptops, but has also been used with Tualatin-M Pentium III processors. The official naming by Intel is µFCPGA and µPGA479M.

Socket P

The Intel Socket P (mPGA478MN) is the mobile processor socket replacement for Core microarchitecture chips such as Core 2 Duo. It launched on May 9, 2007, as part of the Santa Rosa platform with the Merom and Penryn processors.

Quad Flat No-leads package

Flat no-leads packages such as quad-flat no-leads (QFN) and dual-flat no-leads (DFN) physically and electrically connect integrated circuits to printed circuit boards. Flat no-leads, also known as micro leadframe (MLF) and SON, is a surface-mount technology, one of several package technologies that connect ICs to the surfaces of PCBs without through-holes. Flat no-lead is a near chip scale plastic encapsulated package made with a planar copper lead frame substrate. Perimeter lands on the package bottom provide electrical connections to the PCB. Flat no-lead packages include an exposed thermal pad to improve heat transfer out of the IC. Heat transfer can be further facilitated by metal vias in the thermal pad. The QFN package is similar to the quad-flat package (QFP), and a ball grid array (BGA).

Package on package (PoP) is an integrated circuit packaging method to combine vertically 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 route signals between them. This allows higher component density in devices, such as mobile phones, personal digital assistants (PDA), and digital cameras.

Socket 495 CPU socket for Intel mobile processors

Socket 495, sometimes referred to as µPGA2 is a CPU socket for the Intel Pentium III and Celeron mobile processors. This socket was also used in Microsoft's Xbox Console, but in a BGA format. This socket replaced Socket 615 (µPGA1), which was used in Pentium II and early Celeron mobile processors.

Socket G1

Socket G1, also known as rPGA 988A, is Intel's CPU socket for their line of mobile Core i7, the successor to the Core 2 line. It is based on Intel's Nehalem architecture which was first available for the 1366-pin "Socket B", which, like its predecessor, LGA775, uses the LGA socket configuration. Later followed the updated LGA-1156 socket, which moved the QPI and PCI-express controller off the Northbridge and onto the CPU. As a result of the lower pin count, LGA-1156 systems, and later, socket G1 systems, can only run in Dual-channel memory mode, as opposed to the Triple-channel mode which is unique to the LGA-1366 platform. The Nehalem's mobile variant was released on September 23, 2009 in the form of the i7-720QM, 820QM, and 920XM models, followed by the i7-740QM, 840QM, and 940XM models on June 21, 2010. The newer CPUs use the new Clarksfield core, which maintained the same 45 nm manufacturing process as the desktop-based Nehalems. Nehalem received a die shrink on January 7, 2010, under the core name of Westmere. With the Intel GMA HD Graphics Ironlake core packaged onto the CPU substrate, but not integrated directly to the processor die, it goes on to create the Arrandale-based line. The current CPUs to use this package are the Core i7-6x0M series, the Core i5-4x0M series, the Core i5-5x0M series, the Core i3-3x0M series, and finally the Pentium P6x00 series and Celeron P4x00 series which were released on March 28, 2010. However, not all of these are available for Socket G1, as some of them are only available in a BGA package. They are also known as PGA988 socket processors.

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.

Digital image correlation analyses have applications in material property characterization, displacement measurement, and strain mapping. As such, DIC is becoming an increasingly popular tool when evaluating the thermo-mechanical behavior of electronic components and systems.

References

  1. Soldering 101 - A Basic Overview
  2. Alpha (2010-03-15) [September 2009]. "Reducing Head in Pillow Defects - Head in pillow defects: causes and potential solutions". 3. Archived from the original on 2013-12-03. Retrieved 2018-06-18.
  3. "TEERM - TEERM Active Project - NASA-DOD Lead-Free Electronics (Project 2)". Teerm.nasa.gov. Retrieved 2014-03-21.
  4. 1 2 Solid State Technology: BGA underfills - Increasing board-level solder joint reliability, 12/01/2001
  5. "CT Services - Overview." Jesse Garant & Associates. August 17, 2010. "Archived copy". Archived from the original on 2010-09-23. Retrieved 2010-11-24.CS1 maint: Archived copy as title (link)
  6. "Dye and Pry of BGA Solder Joints" (PDF). cascade-eng.com. 2013-11-22. Retrieved 2014-03-22.
  7. Sparkfun tutorials: Reflow skillet, July 2006
  8. Design Requirements - Fine Pitch Ball Grid Array Package (FBGA) DR-4.27D, jedec.org, MAR 2017
  9. Ryan J. Leng. "The Secrets of PC Memory: Part 2". 2007.
  10. Intel. "Mobile Intel Celeron Processor (0.13 μ) in Micro-FCBGA and Micro-FCPGA Packages". Datasheet. 2002.
  11. FCBGA-479 (Micro-FCBGA)
  12. "More than just digital quilting: The "maker" movement could change how science is taught and boost innovation. It may even herald a new industrial revolution". The Economist. Dec 3, 2011.