Semiconductor Package Substrate Joining via Dummy Copper-Core Solder Balls
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Solution Overview
Problem
In semiconductor packages using copper-core solder balls as spacer members, the melted solder can intrude into weak-adhesion areas during reflow, causing short-circuits due to thermal expansion and increased pressure within the mold resin.
Innovation Solution
The manufacturing method involves using dummy copper-core solder balls with a larger amount of solder to initially join the substrates, which are then removed, leaving only a minimal amount of solder within the mold resin, preventing solder intrusion into weak-adhesion areas.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If copper-core solder balls are used as spacer members to join upper and lower substrates, then the substrates can be electrically connected and the distance between them can be maintained constant, but the solder may intrude into weak-adhesion portions during reflow causing short-circuits
Solution Approach 1:
The substrate is divided into a package substrate and a lead frame substrate that are joined separately. The copper-core solder balls are used to join these two substrates, establishing electrical connections without confining large amounts of solder within the mold resin, thereby preventing short-circuits while maintaining electrical connectivity.
Solution Approach 2:
The lead frame is extracted from the traditional substrate structure and treated as a separate substrate component. This allows the copper-core solder balls to join the package substrate and lead frame substrate externally, removing the harmful effect of confined solder expansion from the internal package structure.
2Manufacturing precision
If copper-core solder balls are used to maintain constant distance between substrates, then the interval can be controlled precisely, but thermal expansion of solder increases pressure within mold resin
Solution Approach 1:
The joined structure is segmented into externally connected substrates rather than a single integrated structure. The copper-core solder balls provide precise spacing and distance control between the package substrate and lead frame substrate, while the segmented design allows thermal expansion pressure to be distributed and managed rather than confined.
3Strength
If substrates are joined using copper-core solder balls with sufficient solder amount, then strong electrical connection is achieved, but excess solder is confined within mold resin causing adhesion problems
Solution Approach 1:
The joining operation is extracted from the internal package structure and performed externally between the package substrate and lead frame substrate. This ensures that only the necessary amount of solder is used for strong electrical connection, while excess solder is not confined within the mold resin, preventing adhesion failures.
Solution Approach 2:
The copper-core solder balls act as intermediary elements that join the package substrate and lead frame substrate. They provide the necessary electrical connection and mechanical strength while their external placement ensures that solder confinement does not interfere with mold resin adhesion to the substrates.
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
This approach prevents short-circuiting by minimizing the amount of solder confined within the mold resin, ensuring reliable electrical connections and preventing solder intrusion into weak-adhesion areas, even during thermal expansion.
Implementation Method 1
If the copper-core balls are heated at a temperature at which the solder is melted in the circumference of the copper-core balls, the copper-core balls and the solder are subjected to thermal expansion, and, thereby, a volume thereof tends to increase.
Data Source
AI summary
Conductive core balls are joined to joint pads formed on an upper substrate. Core balls are joined to joint pads formed on an extending part of an upper-substrate substrate material. The joint pads formed on the extending part of the upper-substrate substrate material are joined to the joint pads formed on an extending part of a lower-substrate substrate material via the core balls. The joint pads formed in an area corresponding to the upper substrate of the upper-substrate substrate material are connected to the joint pads formed in an area corresponding to a lower substrate of the lower-substrate substrate material via the core balls and the conductive core balls. The upper-substrate substrate material is fixed to the lower-substrate substrate material by a mold resin supplied therebetween. The extending parts of the upper-substrate substrate material and the lower-substrate substrate material are removed, and the semiconductor packages are individualized.