Metal Paste CTE Matching for PoP Warpage Control
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Solution Overview
Problem
Conventional Package-on-Package (PoP) structures experience significant warpage due to mismatched Coefficients of Thermal Expansion (CTEs) between materials, leading to manufacturing challenges.
Innovation Solution
The application of a metal-containing paste with a CTE greater than the underlying device die, which is cured and acts as an adhesive and stress balancer, along with a molding compound that molds the device die, helps reduce warpage by balancing thermal stresses across the package.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional PoP bonding process is used with molding compound covering solder balls, then packaging is achieved, but significant warpage occurs due to CTE mismatch between materials
Solution Approach 1:
The patent applies a metal-containing paste with specifically engineered CTE parameters that match the device die, creating a stress-balancing layer. This parameter matching approach compensates for the CTE mismatch between the molding compound and device die, reducing warpage while maintaining package bonding reliability
Solution Approach 2:
The patent uses a composite metal-containing paste comprising metal particles (such as tungsten, molybdenum, or nickel) dispersed in a glass-containing matrix material. This composite structure provides both mechanical adhesion and CTE matching properties, enabling stress balance across the package structure during thermal cycling
2Shape
If metal-containing paste with CTE greater than device die is applied, then warpage is reduced through stress balancing, but additional manufacturing steps are required
Solution Approach 1:
The patent combines multiple functions into the metal-containing paste layer: it serves as an adhesive bonding layer, a stress-balancing layer through CTE matching, and a protective layer. This merging of functions reduces the need for separate stress-management layers or complex compensation mechanisms, simplifying the overall device structure despite the additional paste application step
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
This approach effectively reduces warpage in the resulting PoP package by aligning the CTEs of the metal-containing paste and package substrate with the device die, providing sufficient support and stress balance.
Implementation Method 1
There is significant mismatch between the Coefficients of Thermal Expansion (CTEs) of the materials in the PoP packages. The metal-containing paste is specifically formulated to have a CTE that matches the device die, balancing the thermal stresses
Implementation Method 2
A molding compound is applied on the bottom package, with the molding compound covering the second device die and the solder balls
Data Source
AI summary
A package includes a bottom substrate and a bottom die over and bonded to the bottom substrate. A metal-particle-containing compound material is overlying a top surface of the bottom die, wherein the metal-particle-containing compound material comprises metal particles. A molding material molds at least a lower part of the bottom die therein, wherein the molding material is overlying the bottom substrate.