Semiconductor Package Anchor Pad Layout for PCB Thermal Fatigue
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Solution Overview
Problem
Semiconductor packages attached to PCBs via leads are susceptible to thermal fatigue and plastic strain, leading to potential failure due to insufficient robustness in existing soldered joints.
Innovation Solution
Incorporation of an anchor pad that extends across the die and is coupled to the die paddle, providing an additional attachment point to the PCB, along with displaced leads and an encapsulant to enhance connection robustness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If semiconductor packages are attached to PCB via leads only, then the attachment method is simple, but the soldered joints are susceptible to thermal fatigue and plastic strain leading to failure
Solution Approach 1:
The attachment structure is segmented into multiple independent attachment points: traditional leads for electrical connection and a separate anchor pad for mechanical support. This segmentation allows each component to specialize - leads handle electrical signals while the anchor pad bears mechanical stress, resolving the contradiction between simple attachment and joint robustness
Solution Approach 2:
The anchor pad extends in a direction perpendicular to the lead arrangement, adding a new spatial dimension to the attachment structure. This dimensional addition provides an extra attachment pathway that doesn't interfere with the existing lead-based electrical connections, thereby improving reliability without significantly increasing complexity
2Reliability
If an anchor pad is added to provide additional attachment point, then thermal fatigue performance improves, but package size increases
Solution Approach 1:
The anchor pad is designed to serve multiple functions simultaneously: it provides mechanical attachment to the PCB, acts as a heat dissipation path, and serves as a reference element for alignment during assembly. This multi-functionality allows the package to improve thermal fatigue performance without proportionally increasing package footprint
Solution Approach 2:
The anchor pad is merged with the encapsulant structure, where the encapsulant material itself forms part of the anchor pad assembly. This integration eliminates the need for separate anchor pad components, reducing overall package footprint while maintaining improved thermal fatigue performance
3Reliability
If displaced leads are used to act as stress reliever, then board level reliability improves, but manufacturing complexity increases
Solution Approach 1:
The leads are designed with displacement capability, allowing them to dynamically adjust their position in response to thermal expansion and contraction during operation. This dynamic behavior enables the leads to act as stress relievers, absorbing mechanical stress while maintaining electrical connectivity, thereby improving board level reliability despite increased manufacturing complexity
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
Improves thermal fatigue performance and reduces stress on leads and solder joints, ensuring reliable attachment and heat dissipation, while maintaining the overall package size and allowing for inspection and alignment verification.
Implementation Method 1
an encapsulant which at least partly surrounds the die
Implementation Method 2
a die paddle; a die coupled to the die paddle... ensuring reliable attachment and heat dissipation
Data Source
Figure 1~3
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AI summary
There is disclosed a semiconductor package for a PCB. The semiconductor package comprises a die paddle, a die, a connector, an anchor pad and an encapsulant. The die is coupled to the die paddle. The connector is coupled to the die, the connector comprising a plurality of leads for attachment to the PCB. The anchor pad is for attachment to the PCB. The encapsulant at least partly surrounds the die. The anchor pad extends across at least part of the die.