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Lead-Free Ball Grid Array Ball Attachment on a Protruded Copper Pad to Improve Solder Joint Reliability

IP.com Disclosure Number: IPCOM000130520D
Publication Date: 2005-Oct-25
Document File: 3 page(s) / 22K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method that increases the ball grid array (BGA) copper pad surface area, by maximizing the amount of protruded cubic copper column on each of the BGA copper pads. Benefits include improving thermal fatigue reliability and packaging performance.

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Lead-Free Ball Grid Array Ball Attachment on a Protruded Copper Pad to Improve Solder Joint Reliability

Disclosed is a method that increases the ball grid array (BGA) copper pad surface area, by maximizing the amount of protruded cubic copper column on each of the BGA copper pads. Benefits include improving thermal fatigue reliability and packaging performance.

Background

Increased power/ground and signal pins on FCBGA packaging has been achieved by decreasing the ball pitch. The reduction of ball pitch drives the reduction of ball diameter, allowing a smaller contact area between the solder balls and a package’s copper pads. As a result, stresses experienced by the package-to-ball interface are higher, posing technical challenges in solder joint reliability (SJR) performance. Brittle solder joint failure occurs when a package is subjected to high mechanical stresses during shock testing. Thermal fatigue failure occurs after a package is subjected to temperature cycling reliability stresses.

Currently, this problem is addressed by the following:

§         Using large diameter solder balls to produce higher stand-off and more contact areas, which can better distribute the loads and reduce shear stress at the BGA interface. However, this is a shortcoming for fine pitch packages, promoting solder bridging electrical short failures.

§         Increasing the package solder resist opening (SRO) and board pad size, while keeping the optimum aspect ratio. However, this is a drawback for packages requiring high routing density, especially in fine pitch BGA technology.

§         Applying a package corner de-populated BGA ball pattern or a sacrificial ball concept on the fully-populated ball pattern for enhanced mechanical support; however, this restricts
package routing.

§         Evaluating new fluxes to improve solder joint metallurgy (e.g. controlling the growth of the inter-metallic compound and eliminating the phosphorus-rich layer). However, this involves extensive development processes.

General Description

The disclosed method optimizes the FCBGA packaging SJR performance by strengthening both the brittle joint (post shock testing) and thermal fatigue (post temperature...