Heat Sink Adhesive Thickness for Solder Ball Reliability
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Solution Overview
Problem
In semiconductor devices using flip chip bonding, stress concentration at solder balls due to temperature cycling leads to breakage, particularly those overlapping with the flange adhesive layer, compromising reliability and product lifetime.
Innovation Solution
A semiconductor device design with a heat sink having a thicker second adhesive layer (at least twice the thickness of the first adhesive layer) to reduce stress and improve reliability, where the heat sink's flange portion is bonded to the wiring substrate with a second adhesive layer that is thicker than the chip adhesive layer, enhancing stress relaxation and heat dissipation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a heat sink is bonded to the wiring substrate via a flange adhesive layer, then the heat sink is fixed securely, but stress concentration occurs at solder balls overlapping with the flange adhesive layer during temperature cycling
Solution Approach 1:
The patent changes the thickness parameter of the flange adhesive layer, making it at least twice as thick as the chip adhesive layer. This parameter modification allows the adhesive layer to better absorb and distribute thermal expansion stress, preventing stress concentration at the solder balls while maintaining secure bonding of the heat sink to the wiring substrate.
2Use of energy by moving object
If the flange adhesive layer is made thinner for better heat dissipation, then heat transfer efficiency improves, but stress concentration and solder ball breakage increase
Solution Approach 1:
The patent optimizes the thickness parameter of the flange adhesive layer to be at least twice that of the chip adhesive layer. This creates an optimal balance where the adhesive layer is thick enough to absorb thermal stress and protect solder balls, yet thin enough to maintain acceptable heat dissipation efficiency through the adhesive path.
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 increased thickness of the adhesive layer significantly extends the product lifetime by reducing stress and preventing solder ball breakage, thereby enhancing the reliability and durability of the semiconductor device under temperature cycling loads.
Implementation Method 1
the semiconductor chip and the heat sink are bonded to each other via an adhesive layer (chip adhesive layer) that functions as a heat dissipation path
Implementation Method 2
a second portion located around the first portion and fixed to the wiring substrate via a second adhesive layer
Data Source
AI summary
A semiconductor device according to one embodiment, includes: a wiring substrate having a core insulating layer; a semiconductor chip mounted on an upper surface of the wiring substrate; a plurality of solder balls formed on a lower surface of the wiring substrate; and a heat sink having a first portion fixed to a back surface of the semiconductor chip via a first adhesive layer, and a second portion located around the first portion and fixed to the wiring substrate via a second adhesive layer. Here, a portion of the plurality of solder balls is arranged at a position overlapping with each of the second portion of the heat sink and the second adhesive layer. Also, a second thickness of the second adhesive layer is greater than two times a first thickness of the first adhesive layer.