Lead Frame Layout for High-I/O QFP Encapsulation
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Solution Overview
Problem
Current Quad Flat Package (QFP) designs are limited by the number of I/Os due to the peripheral location of outer leads, where about 50% of the metal sheet is used to form electrically isolated leads, restricting the number of leads that can be formed in the lead frame, which is insufficient for advanced technologies requiring more signal transmission.
Innovation Solution
A lead frame design where holes are punched around the periphery of the die pad, with alternating cuts and bends to create inner and outer leads, allowing for a higher number of leads to be formed without punching out sections between leads, resulting in a dam bar effect during encapsulation to prevent leakage and enable more I/Os.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If traditional QFP designs with peripherally located outer leads are used, then the structure is simple and easy to manufacture, but the number of I/Os is limited
Solution Approach 1:
The lead frame is segmented into inner leads and outer leads with distinct functions. Inner leads extend to the periphery for mounting, while outer leads extend beyond the encapsulant for additional I/Os. This segmentation allows different lead types to serve different purposes, increasing the total number of leads without compromising structural integrity
Solution Approach 2:
The patent extends leads in multiple dimensions: inner leads extend to the periphery in one dimension, while outer leads extend beyond the encapsulant in another dimension. This multi-dimensional arrangement maximizes the use of available space and increases the number of I/Os without significantly increasing device footprint
2Quantity of substance
If 50% of metal sheet is stamped or etched out to form electrically isolated leads, then leads are electrically isolated, but the number of leads that can be formed is limited
Solution Approach 1:
The patent merges the functions of lead isolation and lead formation by using a continuous metal sheet for inner leads and selectively removing material only where needed for outer leads. This approach reduces overall material loss while maintaining electrical isolation where required
Solution Approach 2:
Material is extracted (punched out) only in specific locations to form outer leads that extend beyond the encapsulant, rather than removing 50% of the metal sheet. This selective extraction minimizes material loss while still achieving the desired lead configuration and electrical isolation
3Quantity of substance
If holes are punched around the periphery of the die pad with alternating cuts and bends, then inner and outer leads are created, but the manufacturing process becomes more complex
Solution Approach 1:
Holes are punched around the periphery of the die pad in advance, before the encapsulation process. This preliminary action creates the structural framework for both inner and outer leads, allowing subsequent bending and forming operations to proceed more efficiently
Solution Approach 2:
The lead frame fabrication process is segmented into distinct operations: punching holes, making alternating cuts, and bending leads. This segmentation allows each operation to be optimized independently and performed by specialized equipment, reducing overall manufacturing complexity despite the increased number of steps
4Quantity of substance
If alternating cuts and bends are made to create inner and outer leads, then the number of I/Os increases, but encapsulant leakage may occur
Solution Approach 1:
A dam bar structure is introduced as an intermediary element between the inner leads and the encapsulant. This dam bar prevents encapsulant leakage by creating a physical barrier that blocks the flow of encapsulant material, while still allowing the outer leads to extend beyond the encapsulant for additional I/Os
Data Source
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AI summary
A method of making a packaged integrated circuit device includes forming a lead frame with leads that have an inner portion and an outer portion, the inner portion of the lead is between a periphery of a die pad and extends to one end of openings around the die pad. The outer portion of the leads are separated along their length almost up to an opposite end of the openings. Leads in a first subset of the leads alternate with leads in a second subset of the leads. The inner portion of the first subset of the leads is bent. The die pad, the inner portion of the leads, and only a first portion of the openings adjacent the inner portion of the leads are encapsulated. A second portion of the openings and the output portions of the leads form a dam bar for the encapsulating material.