Leadframeless Power Package With Brazed Copper Leads and SiN Substrate
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Solution Overview
Problem
Existing power semiconductor packages (PSPs) rely on leadframes for electrical connections and heat dissipation, which are costly and require additional manufacturing steps, and the introduction of DBC substrates eliminates the need for a die attach paddle but still requires leads, complicating the manufacturing process.
Innovation Solution
A leadframeless power semiconductor package using a substrate with alternating copper and silicon nitride layers, connected via active metal brazing, and silver sintered paste, manufactured using a novel transfer mold with a pinchbar to prevent encapsulant bleeding, eliminating the need for leadframes and soldering.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a leadframe is used to carry electrical signals and dissipate heat, then electrical connections and thermal management are achieved, but manufacturing cost increases and device complexity increases
Solution Approach 1:
The patent extracts and eliminates the leadframe component from the power semiconductor package, retaining only the essential copper leads for electrical connections while removing the complex leadframe structure. This reduces device complexity and manufacturing cost while maintaining electrical connection functionality through direct bonding of copper leads to the substrate.
2Temperature
If a DBC substrate is used to dissipate heat, then thermal performance improves and the die attach paddle becomes unnecessary, but the manufacturing process becomes more complex
Solution Approach 1:
The patent merges the substrate and heat dissipation functions into a single integrated copper lead structure. The copper leads serve both as electrical connections and as heat dissipation pathways, eliminating the need for separate DBC substrate and die attach paddle components, thereby simplifying the manufacturing process while maintaining thermal performance.
3Ease of manufacture
If leadframe components are eliminated to reduce cost, then manufacturing cost decreases, but manufacturing precision requirements increase
Solution Approach 1:
The patent applies preliminary action by pre-attaching the copper leads to the substrate using eutectic bonding before the encapsulation process. This pre-attachment ensures precise alignment and positioning of the leads relative to the substrate, eliminating the need for complex leadframe structures and reducing manufacturing precision requirements during subsequent encapsulation steps.
4Reliability
If solder connections are eliminated to improve reliability, then system reliability improves, but alternative bonding methods must be used
Solution Approach 1:
The patent changes the bonding parameters by using eutectic bonding at lower temperatures without solder, achieving reliable metallurgical bonds between copper leads and the substrate. This parameter change eliminates the need for solder connections and associated lead-free soldering processes, improving system reliability while maintaining manufacturing feasibility through controlled thermal and chemical bonding conditions.
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
The solution reduces manufacturing costs, improves system reliability, enhances current carrying capability, controls warpage, and increases thermal performance by eliminating leadframes and solder connections, while utilizing a high-performance silicon nitride substrate for better thermal conductivity and reduced ceramic cracking.
Implementation Method 1
The copper leads, which are not part of a leadframe, are connected to the substrate using active metal brazing.
Implementation Method 2
The die, which contains circuitry to allow the PSP to operate, is connected to the substrate using silver sintered paste.
Data Source
AI summary
A lead-free power semiconductor package (PSP) includes a substrate, multiple copper leads, a die, and an encapsulant. The substrate has alternating layers of copper and silicon nitride. The copper leads, which are not part of a leadframe, are connected to the substrate using active metal brazing. The die, which contains circuitry to allow the PSP to operate, is connected to the substrate using silver sintered paste. The encapsulant encases the substrate and the die with a portion of the multiple leads being outside the encapsulant.