Induction Heating Pad for Localized Solder Reflow
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Solution Overview
Problem
Conventional reflow processes for semiconductor packages lead to thermal stress and reliability issues due to differences in thermal expansion coefficients between semiconductor chips and mounting substrates, causing adhesion failures and substrate warping.
Innovation Solution
A mounting substrate with an induction heating pad adjacent to a bonding pad, where the induction heating pad is selectively heated by an alternating magnetic field to reflow solder balls, reducing thermal stress and preventing substrate warping by transferring heat efficiently through the bonding pad.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional reflow process is used to mount semiconductor chip, then solder ball reflow is achieved, but thermal stress concentrates in solder ball causing reliability deterioration
Solution Approach 1:
The heating function is segmented from the entire substrate to a localized induction heating pad positioned adjacent to the bonding pad. This localized heating approach concentrates thermal energy only where needed (at the solder ball location) rather than heating the entire substrate, thereby reducing overall thermal stress while achieving effective solder reflow
Solution Approach 2:
The induction heating pad provides localized heating with specific spatial and temporal characteristics. By controlling the heating zone to be adjacent to and slightly larger than the bonding pad, the system achieves precise thermal management that refows solder balls without subjecting the entire substrate to high temperatures, thus reducing thermal stress concentration
2Reliability
If conventional reflow process is used to mount semiconductor chip, then solder ball reflow is achieved, but mounting substrate warps causing adhesion failure
Solution Approach 1:
The heating function is segmented from the entire substrate to a localized induction heating pad. This segmentation prevents uniform thermal expansion across the substrate that causes warping, while still achieving sufficient heat concentration at the bonding pad location for solder reflow
Solution Approach 2:
The induction heating pad is designed with a diameter slightly larger than the bonding pad to provide partial heating coverage. This partial heating approach is sufficient for solder reflow without excessive heating of the entire substrate, thereby preventing warping while maintaining adhesion reliability
3Use of energy by moving object
If induction heating pad with diameter greater than skin depth is used, then heating efficiency is improved, but device complexity increases
Solution Approach 1:
The induction heating pad parameters (diameter, thickness, material composition) are optimized based on skin depth calculations for the operating frequency. By setting the diameter greater than skin depth and thickness less than skin depth, the system achieves efficient electromagnetic energy coupling and heating while maintaining manufacturable dimensions
Solution Approach 2:
The induction heating process utilizes electromagnetic field phase transitions and eddy current generation in the conductive heating pad material. The pad dimensions are designed to resonate with the applied alternating magnetic field frequency, maximizing heating efficiency through constructive electromagnetic interference patterns
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 method improves the reliability of semiconductor packages by preventing thermal deformation and adhesion failures during the reflow process, enhancing the durability of the packages during tests like temperature cycling and drop tests.
Implementation Method 1
the induction heating pad being induction heated by an applied alternating magnetic field to reflow the solder ball
Implementation Method 2
The induction heating pad is selectively induction heated in response to a low frequency band of the alternating magnetic field applied to the mounting substrate
Data Source
AI summary
A mounting substrate includes a substrate, a bonding pad and an induction heating pad. The bonding pad is formed on the substrate, and adhered to a solder ball to mount a semiconductor chip on the substrate. The induction heating pad is disposed adjacent to the bonding pad, the induction heating pad being induction heated by an applied alternating magnetic field to reflow the solder ball. The induction heating pad having a diameter greater than a skin depth in response to the frequency of the applied alternating magnetic field is selectively induction heated in response to a low frequency band of the alternating magnetic field. Accordingly, during a reflow process for a solder ball, the semiconductor chip may be mounted on the mounting substrate to complete a semiconductor package without damaging the mounting substrate, to thereby improve the reliability of the completed semiconductor package.