scope:

This document provides users of underfill material with guidance in selecting and evaluating underfill material. Underfill material is used to increase reliability of electronic devices by two methods: alleviate CTE mismatch (between the electronic package and the assembly substrate) and/or increase mechanical strength. Materials used in underfill applications should not adversely affect device reliability (e.g., ionic impurities, alpha emitters) nor degrade electrical performance. When correctly selected and applied, underfill material should increase the life of the assembled solder joints.

Types of underfill materials currently available in the market include:

• Capillary Flow Underfill

• No-Flow/Fluxing Underfill

• Removable/Reworkable Underfill

• Molded Underfill (not within scope of document)

• Wafer Applied Underfill (not within scope of document)

Introduction This guideline covers polymer based underfill materials intended for use in electronic packaging assembly applications to relieve stress on joints that interconnect flip chips (FC), chip scale packages (CSP) and ball grid arrays (BGA) to an interconnecting substrate

Purpose The purpose of this document is to help in identifying underfill materials whose properties are compatible with component assembly joints to reduce thermomechanical stress so that performance of the assembly is enhanced. The additional role of underfill is protecting the device from environmental factors and increasing strength. Materials used in underfill applications should not adversely affect device reliability (no ionic impurities and no alpha emitters) nor degrade electrical performance. Evaluation methods are provided in the document that are intended to be used for assessing underfill material performance in specific applications as well as troubleshooting failures and how to avoid failures. This document represents the compiled knowledge and experience of the IPC Underfill Adhesives for Flip Chip Applications Task Group.