Lead Frame Layout That Prevents Isolated Metal Contacts
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Solution Overview
Problem
Conventional lead frame cutting processes result in isolated metal contacts that cannot be covered with soldering material, necessitating costly X-ray inspections and leading to poor soldering reliability, electrical conductivity, and thermal conductivity.
Innovation Solution
A lead frame design incorporating short connecting bars that electrically connect metal contacts to horizontal long connecting bars, ensuring electrical continuity post-cutting, allowing direct visual inspection of soldering quality and application of a solderable metal layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional cutting process is used on lead frame, then lead frame units are manufactured, but metal contacts become separate islands that cannot be covered with soldering material
Solution Approach 1:
The lead frame is divided into multiple units through cutting, but retaining bars are deliberately kept connected to maintain electrical continuity. The retaining bars are segmented into multiple sections that remain interconnected, ensuring that metal contacts stay electrically connected even after the lead frame is cut into separate units.
Solution Approach 2:
The retaining bars are pre-configured in the lead frame design before cutting occurs. These bars are strategically positioned and connected to metal contacts in advance, so that when cutting happens, the electrical connection is already established and maintained, preventing metal contacts from becoming isolated islands.
2Measurement precision
If X-ray inspection is used to inspect soldering quality, then inspection can be performed, but inspection cost increases
Solution Approach 1:
The retaining bars are designed to be visually distinguishable and expose the metal contacts and soldering quality directly to the outside. This visual exposure allows inspectors to observe soldering quality through direct visual inspection or color changes in the soldering material, eliminating the need for expensive X-ray equipment.
Solution Approach 2:
The retaining bars serve as an intermediary structure that makes the hidden soldering quality visible. By designing the retaining bars to expose metal contacts and solder joints to the outside, they act as a mediator that translates internal soldering quality into externally observable characteristics, enabling low-cost visual inspection.
3Productivity
If metal contacts are isolated after cutting, then lead frame units are separated, but electrical conductivity and thermal conductivity deteriorate
Solution Approach 1:
The lead frame is segmented into multiple units for manufacturing efficiency, but the retaining bars are designed to maintain electrical and thermal connections between segments. The retaining bars are cut into sections but remain electrically connected, allowing individual units to be separated while preserving conductivity pathways.
Solution Approach 2:
The retaining bars merge the electrical and thermal conduction functions with the structural support function. By combining these functions into a single retained structure, the patent ensures that even after cutting, the metal contacts remain electrically and thermally connected to other components through the retained bar sections.
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
Reduces inspection costs, enhances soldering reliability, electrical conductivity, and thermal conductivity by enabling direct visual inspection and ensuring complete coverage of metal contacts with soldering material.
Implementation Method 1
The at least one short connecting bar electrically connects the plurality of metal contacts of one of the plurality of chip package structures to at least one of the plurality of horizontal long connecting bars adjacent thereto
Data Source
AI summary
A lead frame including a plurality of chip package structures and a plurality of horizontal long connecting bars. The plurality of chip package structures each include a chip solderable area, a plurality of metal contacts and at least one short connecting bar. The plurality of metal contacts are electrically connected to the chip solderable area. The at least one short connecting bar is electrically connected to the plurality of metal contacts. The at least one short connecting bar electrically connects the plurality of metal contacts of one of the plurality of chip package structures to at least one of the plurality of horizontal long connecting bars adjacent thereto.