FPC Solder Bump Layout for Higher Height Without Bridging
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Solution Overview
Problem
The increasing number of pins and size of preamplifier ICs in flexible printed circuit boards (FPCs) for hard disk drives (HDDs) pose mounting difficulties due to shape restrictions, and there is a need to secure a desired solder bump height while reducing solder usage and preventing short circuits between adjacent solder bumps.
Innovation Solution
A board design that includes a base material, a wiring pattern, an insulating member, and a covering portion with a solder contact angle larger than the bump forming portion, allowing for the formation of solder bumps with a higher height using less solder, while preventing short circuits by controlling solder distribution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the number of pins and size of preamplifier IC are increased to achieve high-density mounting, then the mounting capacity is improved, but the mounting difficulty increases due to shape restrictions
Solution Approach 1:
The invention divides the solder bump formation process into distinct zones: a bump forming portion with low solder contact angle for solder accumulation, and a covering portion with high solder contact angle to prevent short circuits. This segmentation allows each zone to perform its specific function optimally, enabling high-density mounting while maintaining manufacturability
Solution Approach 2:
The patent applies different surface properties to different regions of the flexible printed circuit board. The bump forming portion has a low solder contact angle (30°-60°) to promote solder wetting and accumulation, while the covering portion has a high solder contact angle (60°-120°) to repel solder and prevent bridging. This local differentiation of surface quality enables simultaneous achievement of high mounting capacity and ease of manufacture
2Loss of substance
If solder amount is reduced to minimize material usage, then the solder consumption is decreased, but the solder bump height becomes insufficient
Solution Approach 1:
The invention changes the critical parameter of solder contact angle to control solder distribution. By setting the bump forming portion contact angle to 30°-60° and the covering portion to 60°-120°, the system achieves optimal solder accumulation in the bump region while preventing solder spread to adjacent areas. This parameter optimization allows reduced solder consumption while maintaining adequate bump height
Solution Approach 2:
The covering portion acts as an intermediary structure that controls solder flow during the reflow process. Its high contact angle property serves as a barrier that redirects solder toward the bump forming portion, ensuring sufficient bump height even with reduced solder quantity. This intermediary mechanism enables material efficiency without compromising manufacturing precision
3Reliability
If solder bumps are formed with higher height to improve connection reliability, then the connection strength is improved, but the risk of short circuits between adjacent bumps increases
Solution Approach 1:
The patent implements local quality differentiation by creating distinct surface energy zones: the bump forming portion with low contact angle (30°-60°) that attracts and holds solder to build height, and the covering portion with high contact angle (60°-120°) that repels solder to prevent bridging. This spatial differentiation of surface properties simultaneously achieves high connection reliability and eliminates short circuit risks
Solution Approach 2:
The invention converts the potential harmful effect of high solder volume (which could cause short circuits) into a beneficial outcome. By using the covering portion with high contact angle as a barrier, the excess solder is redirected to reinforce the bump forming portion, increasing bump height and reliability while the covering portion itself prevents short circuits. The potential harm of solder overflow is transformed into enhanced connection strength
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 solution enables the formation of solder bumps with a higher height than conventional methods using the same amount of solder, while reducing the risk of short circuits and minimizing solder usage, thus addressing the challenges of increasing pin counts and component sizes in HDD applications.
Implementation Method 1
The covering portion is formed of a material having a solder contact angle larger than that of the bump forming portion in the opening, and covers a part of the bump forming portion
Data Source
AI summary
According to an embodiment, a board includes a base material, a wiring pattern, an insulating member, and a covering portion. The wiring pattern is provided on the base material. The insulating member covers the base material and the wiring pattern, and has an opening corresponding to a bump forming portion of the wiring pattern. The covering portion is formed of a material having a solder contact angle larger than that of the bump forming portion in the opening, and covers a part of the bump forming portion.