Stackable Semiconductor Packages With Truncated Reflowed Bumps
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Solution Overview
Problem
Conventional stackable semiconductor device packages face challenges such as large solder balls occupying valuable space, low stacking yields due to inadequate adherence, and susceptibility to bending or warping, which hinder the reduction of footprint area and increase in solder ball density.
Innovation Solution
A manufacturing method involving a substrate with conductive bumps formed from electrically conductive material, truncated to create reflowed conductive bumps that protrude above a molded structure, allowing for improved adherence and reduced area usage, enabling closer spacing and increased density of solder connections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If conventional large solder balls are used to connect stacked packages, then electrical connections are established, but valuable area on the substrate surface is occupied, hindering reduction of footprint area and increase of solder ball density
Solution Approach 1:
The connecting element is divided into multiple segments: a lower portion embedded in the molded structure and an upper protruding portion that extends above the molded structure. This segmentation allows the solder ball to occupy less surface area while maintaining adequate volume for electrical connection, thereby increasing solder ball density without increasing footprint area.
Solution Approach 2:
The connecting element transitions from a conventional spherical shape to an elongated shape with a vertical component. By extending the connecting element in the vertical dimension (above the molded structure), the design reduces the horizontal footprint while maintaining connection functionality, enabling higher density packaging.
2Reliability
If molding material is applied to cover the entire upper surface for protection, then environmental protection is improved, but molding material may overflow onto the substrate surface and contaminate the peripheral portion, reducing stacking yields
Solution Approach 1:
The molded structure is designed with non-uniform thickness: a first thickness in a central region and a second (reduced) thickness in a peripheral region. This local variation in thickness prevents molding material overflow onto the substrate surface while maintaining adequate coverage and protection in the central region, thereby improving stacking yields without contamination.
3Quantity of substance
If the package body has reduced lateral extent to expose more substrate surface, then stacking density is improved, but the assembly becomes prone to bending or warping, creating stresses on solder balls that lead to connection failure
Solution Approach 1:
The package structure combines multiple materials with complementary properties: a substrate unit providing electrical connections, a molded structure providing mechanical support and protection, and connecting elements providing electrical interconnection. This composite structure achieves both the reduced lateral extent needed for high stacking density and the structural rigidity needed to prevent bending and connection failure.
4Reliability
If conventional solder balls are used without protrusion, then manufacturing is simpler, but adherence during reflow is inadequate, leading to low stacking yields
Solution Approach 1:
The connecting elements are pre-formed with a protruding upper portion that extends above the molded structure before the stacking operation. This preliminary formation of the protruding shape ensures adequate adherence during reflow when the top package is stacked, improving stacking yields while using established manufacturing processes.
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 reduces the footprint area, enhances stacking yields, and improves structural rigidity, allowing for a higher density of semiconductor devices within a given space while maintaining reliable electrical connections.
Implementation Method 1
solder balls, including solder balls 124a and 124b, which are initially part of the top package 102 and are reflowed during stacking operations to electrically connect the top package 102 to the bottom package 104
Data Source
AI summary
Described herein are stackable semiconductor device packages and related stacked package assemblies and methods. In one embodiment, a manufacturing method includes: (1) providing a substrate including contact pads disposed adjacent to an upper surface of the substrate; (2) applying an electrically conductive material to form conductive bumps disposed adjacent to respective ones of the contact pads; (3) electrically connecting a semiconductor device to the upper surface of the substrate; (4) applying a molding material to form a molded structure covering the conductive bumps and the semiconductor device; (5) forming a set of cutting slits extending partially through the molded structure and the conductive bumps to form truncated conductive bumps; and (6) reflowing the truncated conductive bumps to form reflowed conductive bumps.