Space Maintaining Layer for Solder Bump Stress Reduction
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Solution Overview
Problem
In manufacturing mounting structures, sealing materials can expand and contract with temperature changes, causing tensile stress that leads to peeling off of solder bumps from the circuit board due to thermal expansion and contraction, resulting in damage and reliability issues.
Innovation Solution
A manufacturing method involving a sheet with a space maintaining layer having a glass transition temperature above 125°C and a coefficient of thermal expansion of 20 ppm/K or less, which is applied to maintain the internal space and reduce thermal expansion, thereby minimizing stress on solder bumps.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a resin sheet is used as sealing material, then the circuit member can be sealed and internal space can be maintained, but the sealing material expands and contracts with temperature changes causing tensile stress that peels off solder bumps from the circuit board
Solution Approach 1:
The patent changes the physical and chemical parameters of the sealing material by specifying a glass transition temperature of 125°C or higher and a coefficient of thermal expansion of 20 ppm/K or less. These parameter changes ensure the material maintains dimensional stability across temperature ranges while remaining flexible enough to seal the circuit member without causing stress-induced damage to solder bumps
Solution Approach 2:
The patent employs composite material design by combining specific resin components (epoxy resin, phenolic resin, or polyimide resin) with controlled molecular structures to achieve both high glass transition temperature and low thermal expansion coefficient. This composite approach allows the sealing material to simultaneously provide mechanical strength, thermal stability, and stress absorption capabilities
2Adaptability or versatility
If the sealing material has high thermal expansion coefficient, then it can accommodate thermal changes, but it causes repeated pulling stress on solder bumps during thermal cycles leading to damage
Solution Approach 1:
The patent optimizes the thermal parameters of the sealing material by establishing specific ranges for glass transition temperature (≥125°C) and coefficient of thermal expansion (≤20 ppm/K). These parameter changes enable the material to adapt to thermal cycling conditions while minimizing differential expansion stresses that would otherwise damage the solder bumps during repeated heating and cooling cycles
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 improves the connection reliability between circuit members by suppressing the expansion of the internal space and reducing the likelihood of solder bump damage and peeling, even under wide temperature ranges.
Implementation Method 1
the space maintaining layer after curing has a glass transition temperature of higher than 125° C.
Implementation Method 2
a coefficient of thermal expansion at 125° C. or lower of 20 ppm/K or less
Implementation Method 3
a sealing step of pressing the sheet against the first circuit member and heating the sheet, to seal the second circuit members so as to maintain the space, and to cure the sheet
Data Source
AI summary
A manufacturing method of a mounting structure, the method including: a step of preparing a mounting member including a first circuit member and a plurality of second circuit members placed on the first circuit member via bumps, the mounting member having a space between the first circuit member and the second circuit member; a step of preparing a sheet having a space maintaining layer; a disposing step of disposing the sheet on the mounting member such that the space maintaining layer faces the second circuit members; and a sealing step of pressing the sheet against the first circuit member and heating the sheet, to seal the second circuit members so as to maintain the space, and to cure the sheet. The bumps are solder bumps. The space maintaining layer after curing has a glass transition temperature of higher than 125° C., and a coefficient of thermal expansion at 125° C. or lower of 20 ppm/K or less.