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Method for a crack resistance structure in a BGA pad

IP.com Disclosure Number: IPCOM000125770D
Publication Date: 2005-Jun-16
Document File: 7 page(s) / 525K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method for a crack resistance structure in a ball-grid array (BGA) pad. Benefits include improved functionality, improved performance, improved reliability, and improved ease of implementation.

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Method for a crack resistance structure in a BGA pad

Disclosed is a method for a crack resistance structure in a ball-grid array (BGA) pad. Benefits include improved functionality, improved performance, improved reliability, and improved ease of implementation.

Background

              Conventionally, brittle solder joints are a reliability issue in flip-chip ball-grid array (BGA) technology (see Figure 1).

              The technology requires a finer ball pitch to meet cost targets. The reduction in ball pitch increases the risk of brittle solder-joints creating full cracks due to shorter crack propagation paths. The breaking interface for brittle solder joints is at the phosphorous-rich layer (see Figure 2).

              Brittle solder joint cracks usually start from the periphery of a solder joint post shock or vibration stress conditions (see Figure 3).

              Brittle solder-joints break at the phosphorous-rich interface caused by a nickel plating layer. Cracks propagate freely without check to cause full crack failure (see Figure 4).

      The issue of solder-joint brittleness and failure is conventionally solved using the following techniques:

•             New fluxes to improve solder joint metallurgy, such as controlling the growth of intermetallic compound and eliminating the phosphorus-rich layer. However, this solution involves extensive development processes.

•             Solder balls with a larger diameter. However, fine-pitch packages require smaller solder balls. Additionally, solder bridging electrical-short failures can occur from the close placement of larger solder balls.

•             Increasing the package solder-resist opening (SRO) and board pad size but retaining the optimum aspect ratio. However, this solution is unacceptable for packages requiring high routing density, especially in fine-pitch BGA technology.

•             Applying package corner depopulated BGA ball patterns or sacrificial (nonfunctional) solder balls. However, this solution restricts package routing.

Description

              The disclosed method is the placement of an o-ring solder resistant structure on BGA pads to hinder brittle solder-joint crack propagation and improve reliability. The method prevents solder cracks from propagating into solder-joint failure. The method can be applied to all the BGA pads of a substrate or only BGA pads located in high-risk areas (see Figure 5).

              The disclosed method d...