Semiconductor Package Reflow Sequencing to Reduce Warping
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Solution Overview
Problem
The semiconductor industry faces challenges in minimizing warping and associated defects, such as cracking or delamination, in integrated circuit packages due to the integration of high-functional density components, which affects the reliability and yield of packaging processes.
Innovation Solution
A method involving a two-step reflow process using low-temperature solder paste and high-temperature solder bumps to form joints between redistribution and interconnect structures, reducing warping by controlling the temperature and composition of the solder materials, thereby improving connection reliability and package stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If high-functional density components are integrated into semiconductor packages, then functionality and integration density are improved, but warping and associated defects (cracking, delamination) increase
Solution Approach 1:
The bonding process is segmented into two distinct reflow stages: a first reflow process at a lower temperature range (200-250°C) and a second reflow process at a higher temperature range (250-300°C). This segmentation allows controlled formation of solder paste joints followed by complete melting and bonding of solder balls, reducing thermal shock and warping while achieving reliable connections for high-density integrated packages
Solution Approach 2:
The invention changes the temperature parameter by implementing a two-step reflow process with different temperature ranges. The first reflow uses 200-250°C to initially bond solder paste, and the second reflow uses 250-300°C to melt solder balls and form strong joints. This parameter change resolves the contradiction by enabling high-density integration while controlling warping through gradual temperature increase
2Strength
If solder paste and solder balls are bonded using a single high-temperature reflow process, then bonding strength is improved, but warping and defects increase
Solution Approach 1:
The bonding process is divided into two sequential reflow operations: first reflow at 200-250°C to bond solder paste to contact pads, then second reflow at 250-300°C to melt solder balls and form final joints. This segmentation achieves strong bonding while minimizing warping by avoiding a single high-temperature shock
Solution Approach 2:
The first reflow process performs a preliminary bonding action by melting solder paste to create initial joints between the interconnect structure and substrate. This preliminary action stabilizes the structure before the second reflow, reducing warping while ensuring subsequent solder ball bonding strength
3Reliability
If bismuth-containing solder paste is used, then bonding reliability is improved, but cost increases
Solution Approach 1:
Bismuth is applied locally and selectively only to the solder paste material that requires enhanced bonding reliability, rather than adding bismuth to all solder materials or the entire package. This local quality approach improves bonding reliability at contact pads while minimizing overall material cost increase
Solution Approach 2:
The invention changes the compositional parameter of the solder paste by incorporating bismuth metal particles (0.1-5 μm size) at controlled concentrations (0.1-5 wt%). This parameter change improves bonding reliability through enhanced wetting and lower melting point characteristics while controlling cost through precise concentration management
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 reduces warping by up to 50% and enhances the reliability and yield of the packaging process, minimizing defects like debonding, delamination, and cracking, while integrating with existing fabrication processes without significant additional cost.
Implementation Method 1
performing a first reflow process at a first temperature that melts the solder paste
Implementation Method 2
performing a second reflow process at a second temperature that melts the solder paste and melts the solder balls
Data Source
AI summary
A method includes forming regions of solder paste on a redistribution structure, wherein the solder paste has a first melting temperature; forming solder bumps on an interconnect structure, wherein the solder bumps have a second melting temperature that is greater than the first melting temperature; placing the solder bumps on the regions of solder paste; performing a first reflow process at a first reflow temperature for a first duration of time, wherein the first reflow temperature is less than the second melting temperature; and after performing the first reflow process, performing a second reflow process at a second reflow temperature for a second duration of time, wherein the second reflow temperature is greater than the second melting temperature.