Semiconductor Package Adhesive Gradient for Reflow Stress Relief
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Solution Overview
Problem
Conventional semiconductor devices face reliability issues during reflow due to thermal stress generated by the difference in thermal expansion coefficients between the circuit substrate and the resin, leading to potential peeling of the resin.
Innovation Solution
A semiconductor device configuration featuring a wiring substrate with an opening, a metal substrate, and a resin with a thermal expansion coefficient different from the substrate, where a metal paste adhesive is used to cover the semiconductor chip and gradually increase in thickness from the center to the side surface, dispersing thermal stress and preventing resin peeling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a resin with a thermal expansion coefficient different from the wiring substrate is used, then the resin can provide effective sealing and protection, but thermal stress is generated during temperature changes causing potential peeling
Solution Approach 1:
The adhesive thickness is made non-uniform, gradually increasing from the center of the opening toward the side surface of the wiring substrate. This creates a gradient structure where the adhesive layer is thinnest at the center and thickest at the edges, allowing differential thermal expansion to be absorbed gradually rather than creating concentrated stress at uniform thickness boundaries.
Solution Approach 2:
The adhesive layer containing metal paste is applied beforehand to the side surface of the wiring substrate and the main surface of the metal substrate, creating a cushioning layer that anticipates and absorbs the thermal stress that will occur during subsequent temperature changes. This pre-positioned adhesive layer with its gradient thickness acts as a stress buffer before thermal cycling begins.
2Ease of manufacture
If the adhesive thickness is uniform, then the manufacturing process is simple, but thermal stress concentrates at the adhesive boundaries causing peeling
Solution Approach 1:
Instead of applying adhesive with uniform thickness, the process creates a gradient thickness distribution where the adhesive layer gradually increases in thickness from the center to the side surface. This can be achieved through controlled application methods that naturally create the gradient, balancing manufacturing feasibility with stress distribution requirements.
Solution Approach 2:
The adhesive layer thickness parameter is changed from a constant value to a spatially varying value. By controlling the thickness parameter to increase gradually from center to edge, the adhesive layer can accommodate thermal expansion differences while maintaining manufacturability through controlled application processes.
3Length of stationary object
If the adhesive layer is thin, then the device profile is low and assembly is compact, but the contact area and adhesion strength are insufficient
Solution Approach 1:
The adhesive layer thickness is optimized locally at different positions: thin at the center to maintain compact profile, and thick at the side surface to maximize adhesion strength and stress distribution. This spatially varying thickness achieves both compactness and strength requirements simultaneously.
Solution Approach 2:
The solution moves from a one-dimensional uniform thickness approach to a two-dimensional gradient thickness distribution. By varying thickness in the radial direction from center to edge, the system achieves multiple objectives: compact overall profile while providing sufficient adhesion area at the boundaries where stress concentration occurs.
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 solution effectively disperses thermal stress and enhances the reliability of the semiconductor device by securing a large contact area for the adhesive, preventing resin peeling during reflow and improving adhesion strength between components.
Implementation Method 1
a resin disposed to cover the semiconductor chip from above the first main surface of the wiring substrate to the inside of the opening on the main surface of the metal substrate, and formed of a material having a thermal expansion coefficient different from that of the wiring substrate
Data Source
AI summary
A semiconductor device includes a wiring substrate including an opening formed to penetrate from a first main surface to a second main surface, and configured to include an insulating material, a metal substrate fixed to the wiring substrate to cover the opening from the second main surface side, a semiconductor chip fixed inside the opening on a main surface of the metal substrate, a resin disposed to cover the semiconductor chip from above the first main surface on the main surface, and formed of a material having a thermal expansion coefficient different from that of the wiring substrate, and an adhesive containing a metal paste disposed between a side surface of the wiring substrate and the main surface, and the resin, in which the adhesive is disposed on the main surface so that a thickness gradually increases from a center side of the opening to the side surface.