Substrate Groove Structure for Reflow Soldering Flux Management
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Solution Overview
Problem
Conventional substrate structures for reflow soldering are prone to solder ball formation and uncontrollable spreading due to excessive solder paste, which can lead to pressure buildup and explosion, especially when the semiconductor chip is mounted with its entire bottom surface in contact with a copper plate, making it difficult to maintain desired mounting states and potentially causing short circuits.
Innovation Solution
A substrate structure with a groove portion that continuously or discontinuously surrounds the solder paste, where the groove's volume is larger than the evaporated flux, preventing pressure buildup and solder spreading, and allowing for secure retention of molten solder within the groove, thus preventing solder ball formation and ensuring accurate chip alignment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a via-hole is provided to collect excess solder paste, then solder ball formation is prevented, but pressure buildup causes explosion and solder scattering
Solution Approach 1:
The via-hole is segmented into two functional zones: an upper collection space for excess solder paste and a lower drainage path leading to the external surface. This segmentation allows the system to both collect solder paste (preventing solder balls) and drain it safely (preventing pressure buildup and explosion) simultaneously.
2Stability of the object's composition
If the entire bottom surface of the semiconductor chip contacts the copper plate, then mounting stability is improved, but no space is available to form a via-hole
Solution Approach 1:
The via-hole structure extends in the vertical dimension (depth) rather than requiring additional horizontal space. By drilling through the substrate thickness, the invention creates collection and drainage spaces in the Z-direction, allowing full bottom-surface contact mounting while still providing via-hole functionality for solder paste management.
3Quantity of substance
If solder paste is applied in excessive amount, then complete coverage is ensured, but solder paste overflows and forms solder balls
Solution Approach 1:
The invention converts the harmful effect of excessive solder paste (overflow and solder ball formation) into a beneficial outcome by providing a designated collection space (via-hole) where the excess paste can be channeled. The overflow is not prevented but redirected to a safe location, transforming the problem of excess paste into a controlled drainage system that prevents solder balls while ensuring complete pad coverage.
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 substrate structure effectively prevents solder ball formation and scattering, maintains accurate chip alignment, and suppresses electric capacitance decrease, ensuring reliable reflow soldering without short circuits by providing a sufficient volume for flux evaporation and molten solder retention.
Implementation Method 1
a volume of a portion of the groove portion, corresponding to a corner of the semiconductor chip to be mounted is larger than any other portions
Implementation Method 2
the surplus solder gravitates toward the remaining conductor inside the via-hole
Data Source
AI summary
This invention provides a substrate structure that can effectively prevent scattering of solder balls which are produced due to explosion attributable to evaporation of flux during reflow soldering, and spreading of molten solder to the surroundings. On a substrate, a semiconductor chip is mounted via solder paste. The substrate is provided with a groove portion which continuously or discontinuously surrounds the solder paste.