Browse Prior Art Database

TESTING OF BALL GRID ARRAYS (BGAS)

IP.com Disclosure Number: IPCOM000008948D
Original Publication Date: 1999-Jan-01
Included in the Prior Art Database: 2002-Jul-25
Document File: 2 page(s) / 112K

Publishing Venue

Motorola

Related People

Hoe Sei Sing: AUTHOR [+2]

Abstract

Ball grid arrays (BGAs) that are packaged for commercial applications can be ceramic capped or globbed. Each of these BGAs typically has a sub- strate that supports multiple circuit layers. Conventionally, vias for connecting these layers are located on the sides of the substrate and are masked, therefore testing I probing of these BGAs when mounted is almost impossible.

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M-LA Technical Developments

TESTING OF BALL GRID ARRAYS (BGAS)

by Hoe Sei Sing and James How Boon Hua

BACKGROUND DESCRIPTION

  Ball grid arrays (BGAs) that are packaged for commercial applications can be ceramic capped or globbed. Each of these BGAs typically has a sub- strate that supports multiple circuit layers. Conventionally, vias for connecting these layers are located on the sides of the substrate and are masked, therefore testing I probing of these BGAs when mounted is almost impossible.

  Testing/probing or measurements of BGAs when mounted has imposed a big challenge for test engi- neers. However, such testing/probing or measurc- ments can be made possible with test pads connected to the vias of a BGA. These test pads can be situated, for example, on the edge of the substrate of the BGA as shown in Figure 1.

test pad PFB

via

Fig. 1 Top corner view of ball grid array

0 Matomh Inc. 1999 77 January 1999

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0 M M-LA

Technical Developments

  For a glob top BGA, dispensing of epoxy will have to be controlled to ensure that it does not cover the test pads. This can be done by defining a dam parameter. A dam is first built with a different epoxy (lower viscosity) on the substrate before dis- pensing glob epoxy into the inner side of the dam. Alternatively, a step can be created around an inner edge of the substrate to act as flow for the epoxy (see Figure 2)

CONCLUSION

  With the addition of these test...