Discrete Power Module Reflow Attachment With Temperature Threshold Control
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Solution Overview
Problem
The existing methods for attaching discrete power modules (DPMs) to a substrate in electric vehicle inverters face issues such as flux residue leading to voids in solder joints and excessive delamination due to high peak temperatures, which can render the DPMs defective or reduce their lifespan.
Innovation Solution
A method involving the use of solder pre-forms with controlled reflowing processes, temperature monitoring, and dynamic adjustments to maintain temperature zones below a threshold, along with the use of alignment fixtures and insulation trays to ensure proper attachment and thermal management during the reflow process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If traditional soldering with solder paste is used to attach DPMs to substrate, then a robust thermal interface and solid mechanical joint can be created, but flux residue is left behind that increases voids in the solder joint
Solution Approach 1:
The harmful flux component is extracted and removed from the joining process by using alternative attachment methods (silver sintering, eutectic soldering, or copper diffusion bonding) that do not require flux, thereby eliminating flux residue and associated voids while maintaining joint strength
Solution Approach 2:
The patent accepts temporary use of attachment methods with lower peak temperature requirements (silver sintering at 217°C, eutectic soldering at 183°C, or copper diffusion bonding at 1085°C) as acceptable short-term solutions that avoid the flux residue problem, even though they require careful temperature control to prevent epoxy delamination
2Strength
If solder materials with higher liquidus temperatures are used to create robust thermal interface, then stronger mechanical joint is achieved, but the liquidus temperatures approach the peak temperature causing excessive epoxy molding delamination
Solution Approach 1:
The patent changes the temperature parameter by using alternative attachment methods with lower peak temperature requirements (silver sintering at 217°C, eutectic soldering at 183°C, or copper diffusion bonding at 1085°C with controlled atmosphere), thereby achieving strong thermal interfaces without exceeding the epoxy molding's peak temperature tolerance of 240-260°C
Solution Approach 2:
For copper diffusion bonding, the patent uses an inert atmosphere (vacuum or protective gas) to enable bonding at lower temperatures (1085°C) without oxidation, and to allow controlled thermal profiles that prevent epoxy delamination while achieving robust thermal and mechanical properties
3Object-generated harmful factors
If silver sintering process is used to attach DPMs to substrate, then flux residue and voids are eliminated, but the process requires precise temperature control below epoxy peak temperature
Solution Approach 1:
The patent implements feedback control by monitoring the temperature during the attachment process and adjusting heating parameters in real-time to maintain the temperature within the safe range (below 240-260°C peak temperature of epoxy molding), ensuring both void-free joints and prevention of delamination
Solution Approach 2:
The patent performs preliminary preparation by selecting attachment methods (silver sintering, eutectic soldering, or copper diffusion bonding) that inherently operate at controlled temperatures below the epoxy degradation threshold, and by preparing the substrate and DPM surfaces in advance to ensure optimal bonding conditions without requiring excessive heat
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 minimizes voids in solder joints and prevents excessive delamination, ensuring robust thermal and mechanical integrity of the DPM-substrate interface, thereby enhancing the reliability and lifespan of the DPMs.
Implementation Method 1
providing heat to the substrate via the base plate
Implementation Method 2
melting the solder pre-forms by providing heat to the substrate via the base plate
Data Source
AI summary
A method of attaching a plurality of discrete power modules (DPMs) to a substrate includes positioning the substrate such that a bottom surface of the substrate opposes a top surface of a base plate. The method includes placing solder pre-forms on a top side of the substrate, placing each DPM on a top surface of a corresponding solder pre-form, and performing a reflowing process. The reflowing process includes melting the solder pre-forms by providing heat to the substrate via the base plate. The method further includes measuring, via at least one sensor, measured temperatures of a plurality of temperature zones of the DPMs during the reflowing process. The method includes determining, via a controller, whether the measured temperatures of the plurality of temperature zones are below a threshold temperature during the reflowing process and maintaining the measured temperatures of the temperature zones below the threshold temperature during the reflowing process.