Concave Post Bump Printed Circuit Board for Fine Pitch Flip Chip Reliability
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Solution Overview
Problem
Conventional Flip Chip Package on Package (FC POP) technologies face challenges with high defect rates and limited design freedom due to solder bridge issues, especially at fine pitches, and are not suitable for pitches below 500 µm or 400 µm, limiting their application in miniaturized mobile devices.
Innovation Solution
A printed circuit board with a concave post bump structure that increases the bonded surface area with solder bumps, allowing for improved bonding reliability and reduced pitch size, enabling high-reliability flip chip structures and semiconductor packages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of moving object
If a conventional SBA method using solder ball is used for POP connection, then the mounting area can be reduced, but short defects are high due to bridge between solder balls in fine pitch
Solution Approach 1:
The patent applies local quality by creating a concave structure specifically at the bump location where solder balls are placed. This localized geometric modification increases the surface area for solder bonding only at the critical connection points, without affecting the overall pitch or mounting area. The concave shape provides a depression that accommodates solder balls more effectively, reducing bridge defects while maintaining fine pitch dimensions.
Solution Approach 2:
The patent utilizes curvature by forming a concave (curved inward) structure on the bump surface. This curved geometry increases the surface area available for solder ball attachment and creates a mechanical interlock effect. The concave curvature allows solder balls to settle into the depression, improving bonding reliability and reducing short circuit defects between adjacent bumps in fine pitch applications.
2Area of moving object
If the pitch size is reduced to 500 µm or less, then the mounting area is reduced, but the yield rate is low due to high short defects
Solution Approach 1:
The concave structure is applied locally at each bump position, allowing fine pitch dimensions to be maintained while improving individual bump reliability. This localized modification enables reduced pitch sizes without proportionally increasing defect rates, as each bump's concave geometry provides enhanced solder ball accommodation and bonding stability.
Solution Approach 2:
The concave curvature at each bump creates a depression that mechanically secures solder balls, preventing them from bridging to adjacent bumps even when pitch is reduced. This geometric feature maintains high yield rates by reducing short circuit defects, enabling successful manufacturing at 500 µm or less pitch while keeping mounting area compact.
3Length of stationary object
If a bump solder is used as package bump, then the chip size is limited, but the degree of freedom in design with spaced distance between packages is limited
Solution Approach 1:
The concave structure is implemented specifically at the bump locations rather than modifying the entire chip or package structure. This localized approach allows designers to maintain standard chip dimensions while gaining enhanced design freedom through improved bump geometry. The concave bumps can accommodate varying pitch requirements and package configurations without constraining overall chip size or layout flexibility.
Solution Approach 2:
The concave curved geometry of the bumps provides design versatility by enabling reliable bonding at various pitch sizes and package configurations. The curved depression structure adapts to different solder ball sizes and positions, giving designers greater freedom in spacing arrangements and package designs without being constrained by fixed bump dimensions.
Data Source
Figure 1~3
Figure 4(a)~4(d)
Figure 5(e)~5(g)
AI summary
Provided are a printed circuit board which can be used as a substrate for a package, a method of manufacturing the printed circuit board, and a semiconductor package using the printed circuit board, the printed circuit board including: a first substrate (10) having a first mounting area for mounting a package substrate and a second mounting area for mounting a semiconductor element; a single layer or multi-layered circuit pattern of the first substrate (10); and a post bump (30; 301) connected to the circuit pattern, provided on an external insulating layer (11) of the first mounting area, and having a concave upper surface.