Bonded Structure Reflow with Two-Stage Vacuum Void Control
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Solution Overview
Problem
Vacuum reflow methods for reducing voids in solder joints often result in solder material scattering and short-circuiting due to excessive pressure reduction, leading to contamination and reliability issues.
Innovation Solution
A reflow process with two pressure stages: an initial reduction to a first pressure before solder alloy melting, followed by a second reduction to an even lower pressure after melting, with specific pressure and time ratios to control void expulsion and minimize solder scattering.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the pressure in the reflow chamber is reduced to a lower level during vacuum reflow, then voids in the joint portion are more easily expelled to the outside, but solder materials are likely to be scattered causing short-circuiting and contamination
Solution Approach 1:
The reflow process is divided into multiple stages with different pressure levels: a first reflow step at a first pressure level and a second reflow step at a second pressure level. This segmentation allows void expulsion to occur at the appropriate time while preventing solder scattering by controlling pressure reduction timing
Solution Approach 2:
The solder alloy is melted at the first pressure level before the pressure is reduced to the second level. This preliminary melting action ensures the solder is in liquid state before vacuum reflow, allowing voids to be expelled effectively without causing solder material scattering
2Reliability
If vacuum reflow is performed to reduce voids in joint portions, then electrical resistance and heat dissipation are improved, but solder material scattering occurs leading to short-circuiting and board contamination
Solution Approach 1:
The reflow process is divided into multiple stages with different pressure levels: a first reflow step at a first pressure level and a second reflow step at a second pressure level. This segmentation allows void expulsion to occur at the appropriate time while preventing solder scattering by controlling pressure reduction timing
Solution Approach 2:
The pressure parameter is changed in two distinct stages during the reflow process. The first pressure level maintains solder stability while the second pressure level facilitates void expulsion, thereby eliminating harmful solder scattering while achieving the desired void reduction for improved electrical and thermal performance
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 method effectively reduces voids in solder joints while preventing solder material scattering, enhancing the reliability and electrical performance of the joined structure.
Implementation Method 1
heating a first member and a solder material while keeping them in contact with each other in a reflow chamber to melt a solder alloy constituting the solder material
Implementation Method 2
the atmosphere in the reflow chamber is reduced so that voids formed in the joint portion are expanded and thus allowed to be easily expelled to the outside of the joint portion
Data Source
Figure 1
AI summary
A method for producing a joined structure according to the present invention includes: a reflow step of heating a first member and a solder material while keeping them in contact with each other in a reflow chamber to melt a solder alloy constituting the solder material, the reflow step including: a first reflow step of melting the solder alloy with an atmosphere in the reflow chamber reduced to a first pressure P1 lower than the atmospheric pressure; and a second reflow step of, after the first reflow step, melting the solder alloy with the atmosphere in the reflow chamber reduced to a second pressure P2 lower than the first pressure P1.