Leadframeless Isolated Power Package With Direct-Bonded Copper Leads
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Solution Overview
Problem
Power semiconductor packages (PSPs) face challenges with the traditional leadframe structure, which includes a die attach paddle (DAP) that is unnecessary with Direct Copper Bonding (DCB) substrates, leading to extra costs and inefficiencies, while still requiring leads for electrical connections.
Innovation Solution
A lead-free PSP design featuring a substrate with alternating copper and silicon nitride layers, active metal brazing, and silver sintered die attach, along with a novel transfer mold using a pinchbar to prevent encapsulant bleeding, eliminating the need for a leadframe and soldering.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a traditional leadframe structure with die attach paddle (DAP) is used, then electrical connections and heat dissipation are achieved, but manufacturing costs increase and structural complexity increases
Solution Approach 1:
The patent extracts and eliminates the die attach paddle (DAP) component from the traditional leadframe structure. By directly bonding copper leads to the DCB substrate, the unnecessary DAP portion is removed, reducing structural complexity while maintaining electrical connection functionality through the substrate itself
Solution Approach 2:
The patent merges the electrical connection function and heat dissipation function into a single integrated DCB substrate structure. The copper leads directly bonded to the substrate serve both purposes, eliminating the need for separate DAP components and reducing overall device complexity
2Reliability
If a traditional leadframe structure with DAP is used, then electrical connections are provided, but manufacturing costs increase due to extra copper DAP portion
Solution Approach 1:
The patent extracts and eliminates the costly copper DAP portion from the leadframe structure. By using direct copper bonding leads that attach directly to the DCB substrate, the unnecessary copper DAP component is removed, reducing material costs while maintaining electrical connection reliability
Solution Approach 2:
The patent discards the traditional leadframe DAP structure in favor of a more efficient direct bonding approach. The copper leads are directly bonded to the substrate without requiring the intermediate DAP structure, eliminating waste of copper material and reducing manufacturing costs
3Reliability
If encapsulant is used to encase substrate and die, then protection is provided, but encapsulant bleeding into lead area causes manufacturing defects
Solution Approach 1:
The patent introduces a pinchbar as an intermediary element during the encapsulation process. This pinchbar temporarily constrains the encapsulant material during molding, preventing it from bleeding into the lead area, and is subsequently removed after encapsulation is complete
Solution Approach 2:
The patent applies preliminary anti-action by using the pinchbar to preemptively counteract the encapsulant's tendency to bleed during the molding process. The pinchbar is positioned in advance to block the flow path of the encapsulant before bleeding can occur, ensuring precise encapsulant placement
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 solution reduces manufacturing costs, improves reliability, enhances current carrying capability, controls warpage, and minimizes ceramic cracking, resulting in better thermal performance and system reliability compared to legacy PSPs.
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
Figure 1A~1C
Figure 1D~1F
Figure 2A~2B
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.