Flexible PCB Pad Reinforcement for Reliable Wire Bonding
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Solution Overview
Problem
Flexible Printed Circuit (FPC) substrates have low rigidity, leading to connection failures during wire bonding due to sinking of bonding pads made of resin with low elastic modulus, which prevents effective load application by capillary bonding.
Innovation Solution
A novel printed circuit board design with a base film made of insulating material, featuring a first electric conductor pattern on the front surface and a second on the back, both covered by insulating films, with the pad portion having increased rigidity through additional conductor patterns or reinforcing layers to prevent sinking during wire bonding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the FPC substrate is made flexible with low rigidity, then the flexibility and bendability are improved, but the bonding pad sinks inward during wire bonding causing connection failure
Solution Approach 1:
The patent applies local quality by creating a reinforcing layer specifically in the pad portion where high rigidity is needed to prevent bonding pad sinking, while the circuit portion maintains its flexible nature. This localized reinforcement resolves the contradiction by providing structural support exactly where required without compromising the overall flexibility of the FPC substrate.
Solution Approach 2:
The patent uses composite materials by combining the flexible base film with a reinforcing layer made of different material properties. This composite structure allows the pad portion to have both the flexibility needed for FPC applications and the enhanced rigidity required to prevent bonding pad deformation during wire bonding, thus resolving the contradiction between flexibility and connection reliability.
2Strength
If a reinforcing material is affixed to the back surface of the FPC substrate, then the overall structural support is improved, but the bonding pad still sinks inward during wire bonding
Solution Approach 1:
The patent applies local quality by placing the reinforcing layer specifically in the pad portion rather than uniformly across the entire substrate. This localized approach provides precise structural support to the bonding pad area, preventing inward sinking during wire bonding while maintaining the flexibility of the circuit portion, thus resolving the contradiction between structural support and bonding pad position stability.
3Adaptability or versatility
If the bonding pad area is made of resin with low elastic modulus, then the flexibility is maintained, but the capillary cannot apply effective load resulting in connection failure
Solution Approach 1:
The patent applies local quality by creating a reinforcing layer with different mechanical properties specifically in the pad portion. This localized change in material properties provides the necessary load application capability for wire bonding while maintaining the flexibility of the surrounding circuit area, thus resolving the contradiction between flexibility and force application capability.
Solution Approach 2:
The patent uses composite materials by combining the flexible resin base film with a reinforcing layer that has higher elastic modulus. This composite structure in the pad portion enables effective load application by the capillary during wire bonding while the overall FPC maintains its flexibility, resolving the contradiction between flexibility and force application capability.
Data Source
AI summary
A printed circuit board capable of reducing or suppressing connection failure includes a base film made of insulating material, an electric conductor pattern formed on a front surface of the base film, and an insulating cover film covering the electric conductor pattern. The printed circuit board also includes a circuit portion with a circuit formed by the electric conductor pattern, and a pad portion with a bonding pad composed of the electric conductor pattern exposed from the insulating cover film. The pad portion has higher rigidity than the circuit portion.