Lead Frame Strip Electrical Isolation via Chemical Etching
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Solution Overview
Problem
Conventional lead frame processing methods face inefficiencies in electrical isolation of shared leads, leading to increased wear on sawing blades, inaccuracy, and higher costs due to smearing of metal materials and lower material utilization.
Innovation Solution
The method involves attaching semiconductor dies to die paddles, covering with molding compound, forming a mask to expose shared leads, etching a gap through the shared leads, and cutting partly through the molding compound around the periphery to electrically isolate the leads, minimizing metal cutting and maintaining the molding compound for structural integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If sawing is used to sever the leads for electrical isolation, then electrical isolation is achieved, but blade wear increases and accuracy decreases
Solution Approach 1:
The patent replaces the mechanical sawing process with a chemical etching process to achieve electrical isolation of leads. The etching process uses chemical solutions to remove metal material, substituting the mechanical blade contact that causes wear and accuracy issues. This allows precise electrical isolation without the drawbacks of sawing through the leads.
Solution Approach 2:
The patent extracts the electrical isolation function from the lead metal itself and performs it through chemical etching of the molding compound. Instead of cutting through the leads to isolate them, the method removes the molding compound material around the leads, achieving isolation without damaging the lead structure or requiring blade contact with the metal leads.
2Reliability
If sawing through metal leads is performed to provide electrical isolation, then isolation is achieved, but metal smearing occurs
Solution Approach 1:
The patent replaces mechanical sawing with chemical etching to eliminate metal smearing. By using chemical solutions to remove the molding compound rather than mechanically cutting through the metal leads, the process avoids the friction and heat that cause copper and other lead materials to smear and contaminate surrounding areas.
Solution Approach 2:
The patent extracts the isolation function from lead cutting and performs it through selective removal of molding compound. The etching process targets only the non-metallic molding material, leaving the metal leads intact and free from smearing, while still achieving the necessary electrical isolation between adjacent leads.
3Reliability
If conventional sawing processing is used for electrical isolation, then isolation is achieved, but cycle time increases
Solution Approach 1:
The patent replaces the time-consuming mechanical sawing process with a faster chemical etching process. The etching can be performed continuously and does not require the slow, incremental material removal of sawing, significantly reducing the cycle time needed to achieve electrical isolation while maintaining reliability.
Solution Approach 2:
The patent performs electrical isolation during the molding process itself rather than as a separate subsequent step. By integrating the etching operation into the molding cycle, the isolation is achieved as part of the primary manufacturing process, eliminating additional cycle time that would be required for separate sawing or isolation operations.
4Reliability
If sawing is used to sever leads, then electrical isolation is achieved, but cost increases
Solution Approach 1:
The patent replaces expensive mechanical sawing equipment and blade consumption with a chemical etching process. The etching process uses standard chemical solutions and can be performed with simpler equipment, reducing capital investment and operational costs while achieving the same electrical isolation reliability.
Solution Approach 2:
The patent extracts the isolation function from lead-cutting operations and performs it through molding compound removal. This eliminates the need for specialized sawing equipment, blade replacement costs, and the waste associated with cutting through valuable lead materials, thereby reducing overall manufacturing costs while maintaining isolation effectiveness.
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 effectively electrically isolates leads with reduced blade wear and cost, maintaining the molding compound for rigidity during processing, and optimizing material utilization by minimizing metal cutting.
Implementation Method 1
The sheet metal is typically exposed to chemical etchants that remove areas not covered by photoresist
Implementation Method 2
covering the unit lead frames including the semiconductor dies with a molding compound
Data Source
AI summary
A lead frame strip includes a plurality of connected unit lead frames, each unit lead frame having a die paddle and a plurality of leads connected to a periphery of the unit lead frame. A semiconductor die is attached to the die paddles. A molding compound covers the unit lead frames, including the semiconductor dies. Prior to testing or other processing of the lead frame strip, a gap is etched into a region of the leads which are shared by adjacent ones of the unit lead frames. The gap extends at least mostly through the shared leads. A partial cut is made in the molding compound around the periphery of the unit lead frames prior to the subsequent processing, including below the gap in the shared leads, to electrically isolate the leads of the unit lead frames.