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METHOD FOR IMPROVING THE RELIABILITY OF BALL GRID ARRAY DEVICES ON FR4 PRINTED CIRCUIT BOARDS

IP.com Disclosure Number: IPCOM000009828D
Original Publication Date: 2000-May-01
Included in the Prior Art Database: 2002-Sep-20
Document File: 2 page(s) / 84K

Publishing Venue

Motorola

Related People

Jay R. Mitchell: AUTHOR

Abstract

This paper describes a method for improving the reliability of Ball Grid Array (BGA) devices on FR4 Printed Circuit Boards (PCB ), by laminating a thin, relatively compliant layer of material on the component side of the PCB between the BGA and the intemal FR4 layers thus relieving the stress build up in the BGA solder joints during thermal cycling.

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MOTOROLA

Technical Developments

METHOD FOR IMPROVING THE RELIABILITY OF BALL GRID ARRAY DEVICES ON FR4 PRINTED CIRCUIT BOARDS

by Jay R. Mitchell

ABSTRACT

This paper describes a method for improving the reliability of Ball Grid Array (BGA) devices on FR4 Printed Circuit Boards (PCB ), by laminating a thin, relatively compliant layer of material on the component side of the PCB between the BGA and the intemal FR4 layers thus relieving the stress build up in the BGA solder joints during thermal cycling.

PROBLEMS ENCOUNTERED BY PLACING BaA DEVICES DIRECTLY ON FR4 PCBS

BGA packages are becoming commonplace in the realm of portable hand held electronics because of their board area and thermal transfer efficiencies.

Although preferred by manufacturing for their high assembly yields, BGA packages are inferior to leaded packages when considering the reliability due to them1a1 cycle fatigue.

The root problem is solder joint failures due to coefficient of thermal expansion (CfE) mismatches between the device substrate (typically ceramic) and the PCB material (typically FR4). In the case of aeronautical environments, the thermal cycles present reduce the life cycles of the PCB assembly to levels that are unacceptable.

DESCRIPTION OF METHOD AND EXPECTED IMPROVEMENTS

This method of relieving the thermal cycling induced stresses in BGA solder joints is accomplished by laminating a thin, compliant layer of material to the component side of the PCB between the BGA and the internal FR4 layers. Ideally, this interface material would exhibit similar electrical properties as the FR4 material while at the same

Motorola. Inc. 2000

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