Semiconductor Stack Alignment via Dummy Pad Solder Balls
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Solution Overview
Problem
Existing stack structures of semiconductor packages face misalignment issues during the reflow process due to melted solder balls, and previous solutions involving pre-solder materials or infrared paste increase fabrication costs and complexity.
Innovation Solution
A stack structure and method where dummy pads on the upper semiconductor package correspond to the encapsulant of the lower package, allowing solder balls to both connect electrically and surround the encapsulant, preventing misalignment without additional fabrication processes or materials like pre-solder or infrared paste.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If solder balls are used to electrically connect and stack semiconductor packages, then electrical connection is achieved, but misalignment occurs during reflow process due to melted and softened solder balls
Solution Approach 1:
The patent applies preliminary action by pre-positioning the solder balls on the substrate before mounting the upper semiconductor package. The solder balls are placed in precise locations corresponding to both electrical connection pads and dummy pads around the encapsulant, establishing a fixed reference framework before the reflow process begins. This pre-positioning ensures that even when solder balls melt during reflow, their original positions serve as alignment guides to prevent misalignment between stacked packages.
2Manufacturing precision
If pre-solder material is disposed on bond pads of substrate to achieve self-alignment, then alignment precision is improved, but fabrication costs and process complexity increase
Solution Approach 1:
The patent extracts the alignment function from the electrical connection solder balls and assigns it to separate dummy pads positioned around the encapsulant. By separating the electrical connection function (performed by solder balls on electrical connection pads) from the alignment function (performed by solder balls on dummy pads), the invention eliminates the need for additional pre-solder materials and complex alignment processes, using only the existing solder balls for both purposes.
3Manufacturing precision
If infrared paste is provided between substrates and infrared irradiation is performed to adhere packages, then alignment is prevented, but fabrication costs and process complexity increase
Solution Approach 1:
The patent applies self-service by enabling the solder balls on dummy pads to automatically perform the alignment and positioning function without requiring external infrared paste or infrared irradiation processes. The solder balls themselves, through their pre-positioned locations and melting behavior during reflow, provide the self-alignment mechanism that eliminates the need for additional adhesion materials and complex infrared processing steps.
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 effectively prevents misalignment and electrical connection failures while reducing fabrication costs and complexity by using solder balls on both electrical and dummy pads to position and secure the upper package on the lower one, eliminating the need for pre-solder materials or infrared paste.
Implementation Method 1
the solder balls become melted and softened during the reflow process
Implementation Method 2
subjected to a reflow process to make the solder balls bonded and electrically connected to the bond pads
Data Source
AI summary
A stack structure of semiconductor packages and a method for fabricating the stack structure are provided. A plurality of electrical connection pads and dummy pads are formed on a surface of a substrate of an upper semiconductor package and at positions corresponding to those around an encapsulant of a lower semiconductor package. Solder balls are implanted to the electrical connection pads and the dummy pads. The upper semiconductor package is mounted on the lower semiconductor package. The upper semiconductor package is electrically connected to the lower semiconductor package by the solder balls implanted to the electrical connection pads, and the encapsulant of the lower semiconductor package is surrounded and confined by the solder balls implanted to the dummy pads. Thereby, the upper semiconductor package is properly and securely positioned on the lower semiconductor package, without the occurrence of misalignment between the upper and lower semiconductor packages.