PCB-Embedded Power Module Assembly With Coplanar Clip Terminals
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Solution Overview
Problem
Power semiconductor modules face challenges with die placement accuracy and contamination issues due to the sensitivity of semiconductor materials like silicon to laser drilling and the presence of ions in PCB processing materials, leading to problems with accurate gate pad contacting and terminal coplanarity in printed circuit boards.
Innovation Solution
A method involving the use of solder paste to attach power semiconductor dies to a leadframe and metal clips, with a hard stop feature for precise alignment and bonding, allowing for the formation of coplanar terminals within +/−30 μm, reducing the complexity of diffusion soldering and avoiding bimetallic bending.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If laser drilling is used to form openings in PCB insulator material, then via formation is achieved, but semiconductor material is damaged due to sensitivity to laser drilling
Solution Approach 1:
The patent applies preliminary action by forming openings in the PCB insulator material before mounting the semiconductor module. This allows the openings to be created when the semiconductor material is not present, eliminating laser-induced damage. The openings are subsequently filled with conductive material to form vias that connect to the semiconductor terminals.
2Strength
If diffusion soldering is used to attach metal clips to terminals, then bonding is achieved, but process complexity increases and bimetallic bending occurs
Solution Approach 1:
The patent extracts the complexity and bimetallic bending issue by replacing diffusion soldering with a simpler solder paste reflow process. The metal clips are attached using standard solder paste applied to pads on the PCB, eliminating the need for complex diffusion soldering equipment and processes while avoiding the thermal expansion mismatch problems that cause bimetallic bending.
3Manufacturing precision
If tight control is applied for interface alignment, then via connection accuracy is improved, but manufacturing complexity increases
Solution Approach 1:
The patent applies preliminary action by pre-forming openings in the PCB at the exact locations where semiconductor terminals will be mounted. The semiconductor module is then designed with terminals that align with these pre-formed openings, eliminating the need for tight control during mounting operations. The hard stop feature further ensures accurate positioning without requiring complex control systems.
4Ease of manufacture
If standard solder processes are used, then manufacturing simplicity is maintained, but die thickness must be increased to ensure reliability
Solution Approach 1:
The patent uses composite materials by combining solder paste with specific PCB substrate materials and metal clip materials. This composite approach allows standard solder reflow processes to be used effectively with thinner semiconductor dies. The metal clips provide mechanical support and thermal management that compensates for the reduced die thickness, enabling the use of standard solder processes without requiring thicker dies.
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 improves die placement accuracy and reduces contamination risks, enabling the use of thinner semiconductor dies and standard solder processes, resulting in power modules with improved tolerance control and reduced warpage, while ensuring proper via formation during PCB embedding.
Implementation Method 1
reflowing the first solder paste and the second solder paste to form a first soldered joint between each first metal clip and the corresponding first load terminal of each power semiconductor die, a second soldered joint between each second metal clip and the corresponding control terminal of each power semiconductor die, and a third soldered joint between the second load terminal of each power semiconductor die and the corresponding substrate section of the leadframe structure
Data Source
AI summary
A power module for PCB embedding includes: a leadframe; a power semiconductor die with a first load terminal and control terminal at a first side of the die and a second load terminal at the opposite side, the second load terminal soldered to the leadframe; a first metal clip soldered to the first load terminal and forming a first terminal of the power module at a first side of the power module; and a second metal clip soldered to the control terminal and forming a second terminal of the power module at the first side of the power module. The leadframe forms a third terminal of the power module at the first side of the power module, or a third metal clip is soldered to the leadframe and forms the third terminal. The power module terminals are coplanar within +/−30 μm at the first side of the power module.