Ball grid array

Ball grid array
Name	Ball grid array
Caption	Bottom view of a BGA package showing the array of solder balls.
Invented	1960s/1970s
First used	1970s
Manufacturer	IBM, Motorola, Citizen Watch
Classification	Surface-mount technology

Ball grid array. A ball grid array is a type of surface-mount packaging used for integrated circuits. It utilizes a grid of solder balls on the underside of the package to provide electrical connections to a printed circuit board. This design offers significant advantages in interconnect density and thermal performance compared to older packaging technologies like the quad flat package or pin grid array.

Overview

The ball grid array emerged as a solution to the limitations of peripheral lead packages, which struggled with the increasing pin count of modern microprocessors and application-specific integrated circuits. Pioneering work on area array interconnection was conducted by companies like IBM in the 1960s, with its use in modules for systems like the IBM 3081. The commercial adoption of BGA technology accelerated in the 1990s, driven by the needs of the personal computer and telecommunications industries. It represented a major shift from packages with leads on the perimeter to those utilizing the entire underside area for connections, enabling more efficient use of printed circuit board real estate.

Construction and design

A standard ball grid array package consists of a substrate, typically made from bismaleimide-triazine resin or similar laminate, upon which the semiconductor die is mounted. The die is connected to the substrate using wire bonding or flip chip techniques. The substrate contains routed traces that fan out the connections from the die to an array of pads on the package's bottom surface. Solder balls, composed of a tin-lead or lead-free alloy like SAC305, are attached to these pads. The entire assembly is often encapsulated with a molding compound for protection. Key design parameters include ball pitch, array size, and substrate layer count, which are optimized for specific electrical and thermal requirements.

Types and variants

Several specialized variants of the ball grid array have been developed. The plastic ball grid array is a common, cost-effective type using an organic substrate. The ceramic ball grid array utilizes a alumina or similar substrate for enhanced thermal and electrical performance in high-reliability applications like military electronics. The tape ball grid array employs a flexible polyimide tape as the substrate. Other notable variants include the micro ball grid array for very fine pitches, the chip-scale package, which is nearly the size of the die itself, and the enhanced ball grid array which incorporates an integrated heat spreader. The land grid array is a related package type that uses flat contacts instead of solder balls.

Applications and advantages

Ball grid array packages are ubiquitous in modern electronics where high performance and miniaturization are critical. They are extensively used in central processing units, graphics processing units, chipsets, and field-programmable gate arrays within devices like PlayStation 2, Xbox (console), and high-end Cisco Systems routers. Primary advantages include a shorter electrical path that improves signal integrity at high frequencies, superior thermal conduction from the die to the printed circuit board, and a higher interconnection density that reduces the package footprint. This allows for more compact and powerful devices compared to those using leadless chip carrier or quad flat package technology.

Manufacturing and assembly

The assembly of ball grid array components onto a printed circuit board is a precise process within surface-mount technology lines. It begins with the application of solder paste to the board's pads using a stencil printing process. The BGA component is then placed by a pick-and-place machine with high accuracy. The entire assembly undergoes reflow soldering in a controlled atmosphere oven, where the solder paste and the component's solder balls melt to form joints. Inspection is challenging due to the hidden joints and typically requires X-ray imaging systems. Rework processes involve specialized tools from companies like OK International to safely remove and replace faulty components.

Reliability and failure modes

While robust, ball grid array assemblies are susceptible to specific failure mechanisms, primarily driven by coefficient of thermal expansion mismatches between the package, solder balls, and printed circuit board. Cyclic thermal stresses during operation can lead to solder fatigue and crack propagation in the solder joints, eventually causing electrical failure. Other concerns include voiding within solder joints, popcorning from moisture absorption, and electromigration. Reliability is rigorously tested under standards from organizations like JEDEC and is a critical consideration in automotive applications for companies like Tesla, Inc. and in aerospace for contractors like Lockheed Martin.

Category:Integrated circuit packaging Category:Electronic engineering Category:Computer hardware