Substrate Strip Warpage Reduction via Reverse Bending Molding
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Solution Overview
Problem
Warpage occurs in substrate strips after the molding process due to shrinkage stress from high polymer molding compounds, organic ingredient hardening, and differing thermal expansion coefficients, causing manufacturing issues.
Innovation Solution
A method involving a base with matching surface curvature to the warped substrate strip, which is contacted during the molding process to apply a counteracting tension stress, thereby reducing warpage by offsetting contraction stress from the molding compound.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a molding compound is heated and wrapped around dies on a substrate strip, then the chip is protected from moisture and air, but warpage occurs in the substrate strip after the molding process
Solution Approach 1:
The patent applies preliminary anti-action by pre-bending the substrate strip in the opposite direction of the expected warpage before the molding process. The substrate strip is bent concavely upward along its length direction to create a counteracting curvature that compensates for the shrinkage stress that will occur during molding, thereby preventing warpage after the process
Solution Approach 2:
The patent employs parameter changes by modifying the temperature parameters during the molding process. The molding compound is heated to a specific temperature range (170-180°C) and then cooled at a controlled rate (3-5°C per minute) to reduce thermal stress and minimize warpage while maintaining chip protection
2Strength
If the molding compound shrinks during cooling, then the compound hardens and protects the die, but shrinkage stress causes warpage in the substrate strip
Solution Approach 1:
The patent applies preliminary anti-action by pre-bending the substrate strip in the opposite direction of the expected warpage before the molding process. The substrate strip is bent concavely upward along its length direction to create a counteracting curvature that compensates for the shrinkage stress that will occur during molding, thereby preventing warpage after the process
Solution Approach 2:
The patent utilizes phase transitions by controlling the temperature-dependent phase change of the molding compound from a soft, moldable state at high temperature to a hardened state during cooling. This controlled phase transition allows the compound to shrink and harden while minimizing stress through proper temperature management
3Ease of manufacture
If the substrate strip is heated during the molding process, then the molding compound softens and wraps around the die, but thermal expansion differences cause warpage
Solution Approach 1:
The patent employs parameter changes by modifying the temperature parameters during the molding process. The molding compound is heated to a specific temperature range (170-180°C) and then cooled at a controlled rate (3-5°C per minute) to reduce thermal stress and minimize warpage while maintaining chip protection
Solution Approach 2:
The patent applies preliminary anti-action by pre-bending the substrate strip in the opposite direction of the expected warpage before the molding process. The substrate strip is bent concavely upward along its length direction to create a counteracting curvature that compensates for the shrinkage stress that will occur during molding, thereby preventing warpage after the process
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
Significantly reduces warpage in substrate strips to a negligible level, improving manufacturing efficiency and productivity by optimizing the temperature rise and drop curve in the molding process.
Implementation Method 1
differing thermal expansion coefficients
Implementation Method 2
shrinkage stress from high polymer molding compounds
Implementation Method 3
apply a counteracting tension stress, thereby reducing warpage by offsetting contraction stress
Data Source
AI summary
A method for reducing warpage occurred to a substrate strip after a molding process is provided. First, several dies are mounted on a top surface of a substrate strip. Then, a base having a top surface with a surface curvature is provided, and the top surface of the base is contacted against a bottom surface of the substrate strip to bend the substrate strip. Next, under the status that the top surface of the base is contacted against the bottom surface of the substrate strip, a molding compound is wrapped around each die. Finally, the molding compound is cooled to a room temperature. Accordingly, the molding process is performed on the substrate strip reversely bent in a direction opposite to a warpage direction. Therefore, the warpage originally caused by the molding process is offset by the reverse bending.