IC Packaging Peel Strip Lead Separation
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Solution Overview
Problem
The existing integrated circuit packaging process faces challenges in increasing lead count, achieving a versatile lead layout, and simplifying manufacturing, particularly due to the complications and risks associated with the partial sawing process used to separate leads, which introduces moisture pathways, mechanical cracks, and limits the ability to create multiple rows of leads.
Innovation Solution
The method involves forming a leadframe with a tiebar and outer lead, attaching it to a peel strip with an inner lead, wire bonding the die to both leads, encapsulating them, and then removing the peel strip to expose the inner lead's bottom surface, allowing for a more efficient and reliable separation of leads without the need for partial sawing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a partial sawing process is used to separate leads, then the leads can be separated, but it creates moisture pathways, mechanical cracks, and increases device failure risk
Solution Approach 1:
The disturbing part (peel strip) is extracted from the system after serving its purpose. The peel strip is removed after molding to expose the inner lead bottom surface, eliminating the need for partial sawing and avoiding the associated harmful effects of moisture pathways and mechanical cracks
Solution Approach 2:
The peel strip serves as an intermediary element that enables lead separation without direct mechanical cutting. It acts as a temporary carrier that allows the inner lead to be formed and positioned, then removed cleanly without damaging other package components
2Quantity of substance
If the lead count is increased by forming leads from the periphery of the die pad, then more leads are available, but the partial sawing process becomes more complex and risky
Solution Approach 1:
The leadframe is segmented into multiple independent leads (inner leads and outer leads) that can be formed and positioned separately using the peel strip method. This segmentation allows for increased lead count without requiring complex partial sawing operations for each lead
Solution Approach 2:
The peel strip structure enables the leads to self-align and self-position during the molding process. The inner leads are formed on the peel strip in their final positions, eliminating the need for complex post-molding separation processes
3Quantity of substance
If two rows of leads are desired, then lead count increases, but two steps of partial sawing are required which dramatically increase risks
Solution Approach 1:
The peel strip method transitions the lead separation problem from a planar cutting operation to a three-dimensional removal process. Multiple rows of leads can be formed on the peel strip in different positions and then all exposed simultaneously by removing the peel strip, avoiding the need for multiple sequential sawing steps
Data Source
AI summary
A method of manufacture of an integrated circuit packaging system includes: forming a leadframe with a tiebar and an outer lead having an outer lead outer pad; forming an inner lead on a peel strip; attaching the leadframe to the peel strip around the inner lead; wire bonding a die to the outer lead and the inner lead; encapsulating the die and portions of the outer lead and the inner lead; removing the peel strip to expose a bottom surface of the inner lead; and removing the leadframe to have the outer lead outer pad of the outer lead coplanar with the bottom surface of the inner lead.