Lead Frame Notch Design for Controlled Bending and Pitch
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Solution Overview
Problem
The existing lead frame technology for integrated circuit packaging faces issues with lead pitch reduction and potential electrical short circuits due to the deformation caused by mold tooling, which can lead to tape separation and contact between Gull Wing and J-leads.
Innovation Solution
Incorporating notches or grooves at predetermined locations on the leads to facilitate controlled bending during the molding process, ensuring that the inner lead areas remain adhered to the tape and preventing adjacent leads from contacting each other, thus maintaining the required lead pitch and preventing short circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If mold tooling presses down on the outer lead side to offset adjacent leads, then lead pitch is reduced and leads are separated at the package body, but the tape separates from the leads causing potential short circuits
Solution Approach 1:
The lead is pre-formed with a notch at a predetermined location before the molding process. This preliminary structural preparation ensures that when the mold tooling applies pressure during packaging, the lead bends at the intended notch location rather than causing tape separation, thus maintaining both lead pitch precision and tape adhesion reliability
Solution Approach 2:
The notch acts as an intermediary structural element that mediates between the mold tooling pressure and the lead-tape assembly. It provides a designated bending point that absorbs the deformation force, preventing the force from transferring to the tape-lead interface and causing separation
2Productivity
If leads are bent to reduce pitch and increase lead density, then more leads can be spaced around the body, but adjacent leads may contact each other causing electrical short circuits
Solution Approach 1:
The notch is pre-positioned on the lead at a location that ensures controlled bending away from adjacent leads during the molding process. This preliminary structural feature guarantees that when leads are deformed to increase density, they bend in a predictable manner that maintains electrical isolation between adjacent leads
Solution Approach 2:
The notch creates a localized bending zone on the lead that concentrates the deformation at a specific point. This local structural modification ensures that the bending occurs precisely where intended, maintaining proper spacing and electrical isolation between adjacent leads while still achieving the desired lead density
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 notch-based lead frame design allows for effective bending of leads without separating the tape, maintaining the inner lead plane and preventing electrical shorts, thereby ensuring compliance with lead pitch requirements and reliable electrical connections.
Implementation Method 1
a first notch formed in a surface of the inner lead area proximate to the outer lead area that facilitates bending of the at least one lead when the at least one lead is subjected to a downward force by a mold tool at the outer lead area
Data Source
AI summary
A lead frame for a packaged integrated circuit (IC) device has a die receiving area and leads that extend outwardly from the die receiving area. The leads have an inner lead area proximate the die receiving area and an outer lead area distant from the die receiving area. Notches are formed in a surface of alternate ones of the leads, in the inner lead area proximate to the outer lead area. The notches facilitate bending of the alternate leads when the leads are subjected to a downward force by a mold tool, such that one set of leads lies in a first plane and another set lies in a second plane spaced from the first plane. The leads in the first plane can be formed into Gull Wing leads and the other set of leads into J-leads.