Circuit Board Protrusion Design for Flip-Chip Thermal Stress
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Solution Overview
Problem
In electronic component devices with flip-chip bonding, thermal stress concentrates on the lower corner portions of connection pads, leading to cracking of the insulating layer and reduced reliability due to the resin layer contacting these areas.
Innovation Solution
A circuit board design featuring an insulating layer with protrusions beneath the connection pads, where the peripheral lower surface of the pads is exposed, preventing the insulating layer from being the origin of cracks and providing structural support for the pads during flip-chip bonding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the insulating layer is formed continuously under the connection pad, then the insulating layer provides electrical insulation, but thermal stress concentration causes cracking at the lower corner portions
Solution Approach 1:
The insulating layer is extracted or removed from the lower corner portions of the connection pad, creating a recessed structure. This removes the source of crack initiation while maintaining insulation where needed. The patent specifically describes etching the insulating layer to form recesses at the lower corner portions, thereby eliminating the harmful insulating layer presence in stress-concentrated areas.
Solution Approach 2:
The insulating layer is treated differently in different locations: it is present in the central region under the connection pad for electrical insulation, but removed in the lower corner portions where thermal stress concentrates. This local differentiation optimizes both insulation function and stress resistance by adapting the insulating layer's presence to the local functional requirements.
2Reliability
If the insulating layer is removed from lower corner portions, then crack resistance is improved, but the connection pad loses structural support
Solution Approach 1:
A reinforcing structure (such as a through-hole conductor or support electrode) is formed in advance in the lower corner portions where the insulating layer is removed. This preliminary reinforcement compensates for the loss of insulating layer support before the connection pad is subjected to thermal stress, ensuring both crack resistance and structural strength are maintained.
Data Source
AI summary
A circuit board includes an insulating layer having a protrusion on a surface, and a connection pad formed on an upper surface of the protrusion. A peripheral portion of a lower surface of the connection pad is exposed from the protrusion.