Underfill Curing Carrier for Flip Chip Warpage Control
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Solution Overview
Problem
High temperatures during underfill curing in flip chip packages lead to significant warpage, causing internal stress and die cracking issues during subsequent processing steps, such as molding compound grinding.
Innovation Solution
An underfill curing method using a carrier with a higher coefficient of thermal expansion than the substrate, where the carrier is bonded over the top dies with an adhesive layer and subjected to a thermal process, allowing for controlled warpage reduction through CTE mismatch and temporary bonding, enabling the carrier's reuse after release layer decomposition.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high temperature curing is applied to the underfill, then the curing effect is improved, but the warpage of the flip chip package increases significantly
Solution Approach 1:
A carrier is introduced as an intermediary component during the curing process. The carrier has a higher coefficient of thermal expansion than the substrate, which allows it to compensate for the warpage caused by thermal expansion mismatch during high temperature curing. The carrier temporarily supports the package structure during curing, then is removed after curing is complete, leaving the underfill properly cured without excessive warpage.
Solution Approach 2:
The invention changes the thermal expansion parameter by selecting a carrier material with a higher coefficient of thermal expansion than the substrate. This parameter difference is deliberately used to counteract the warpage tendency during curing. The carrier's thermal expansion characteristics are specifically chosen to compensate for the substrate-underfill-die assembly's warpage during the curing temperature range.
2Reliability
If high warpage is present, then the underfill curing is achieved, but the internal stress and die cracking risk increase
Solution Approach 1:
The carrier acts as a temporary mediator that maintains package flatness during curing. By supporting the package structure with the appropriately selected carrier, the internal stresses that would otherwise lead to die cracking are minimized during the curing process. The carrier is removed after curing, leaving a cured underfill with reduced internal stress.
3Reliability
If high warpage occurs during curing, then the underfill sets properly, but the wafer handling becomes difficult in subsequent processes
Solution Approach 1:
The carrier serves as a temporary handling aid during curing that ensures the underfill sets properly. After curing, the carrier is removed, leaving the package with minimal warpage that facilitates easy handling in subsequent wafer processing steps such as molding compound grinding. The carrier enables proper curing while not compromising subsequent manufacturability.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The method effectively reduces warpage from 1159 μm to as low as 273 μm, minimizing internal stress and die cracking risks, while allowing for the reuse and recycling of the carrier.
Implementation Method 1
An underfill curing method using a carrier with a higher coefficient of thermal expansion than the substrate
Data Source
AI summary
A method includes bonding a carrier over a top die. The method further includes curing an underfill disposed between a substrate and the top die. The method further includes applying a force over the carrier during the curing. The method further includes removing the carrier from the top die.