Lead Frame Dam for Semiconductor Die Attach Contamination
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Solution Overview
Problem
Current semiconductor assembly processes face contamination issues in the down bond area of lead frames due to die attach material, leading to low wire peel strength, especially in devices with small lead frames and large dies, where space constraints and high costs of half etching pose challenges.
Innovation Solution
A dam is formed between the down bond area and the die attach area on the lead frame, with its bottom attached to the surface, preventing contamination from die attach material, and can be made from materials like Al, Au, or Cu using wire bonding or cured adhesive paste.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a half etching process is used to prevent contamination, then contamination prevention is improved, but manufacturing cost increases and device complexity increases
Solution Approach 1:
The patent uses a disposable dam structure made of inexpensive materials (solder, eutectic alloy, or adhesive) that prevents contamination during assembly. The dam is a simple, low-cost barrier that is applied temporarily during the die attach process and then removed or remains as a non-interfering structure, avoiding the need for expensive half etching processes while effectively preventing die attach material from contaminating the down bond area.
2Object-affected harmful factors
If a half etching process is used to prevent contamination, then contamination prevention is improved, but device complexity increases
Solution Approach 1:
The patent replaces the complex half etching process with a simple dam structure made of inexpensive materials. The dam is applied as a temporary barrier during die attach, preventing contamination without requiring permanent modifications to the lead frame. This approach significantly reduces process complexity while maintaining effective contamination prevention.
3Device complexity
If no barrier is used, then device complexity is reduced, but wire peel strength decreases due to contamination
Solution Approach 1:
The patent introduces a dam structure as an intermediary barrier between the die attach area and the down bond area. This dam acts as a mediator that prevents die attach material from reaching the down bond area, thereby protecting wire peel strength. The dam is made of materials that are compatible with the bonding process and does not interfere with the electrical connection, maintaining simplicity while ensuring reliability.
4Object-affected harmful factors
If space is allocated for groove formation, then contamination prevention is improved, but available device area decreases
Solution Approach 1:
The patent uses a dam structure that can be applied in the existing space between the die attach area and down bond area without requiring additional grooves or etching. The dam acts as a mediator that fits within the available space, preventing contamination while maximizing the use of the lead frame area. This approach is particularly advantageous for devices with small lead frames and large dies where space is limited.
Data Source
AI summary
A semiconductor device includes a lead frame having a down bond area, a die attach area and a dam formed between the down bond area and the die attach area. A bottom of the dam is attached on a surface of the lead frame. The dam prevents contamination of the down bond area from die attach material, which may occur during a die attach process.