Anchor-Shaped Lead Frame Bending Process
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Solution Overview
Problem
The manufacturing of lead frames for high-density semiconductor devices is hindered by the high cost and reduced processing speed associated with wet etching, which also leads to deformation due to stress applied during pressing processes that form anchor shapes in leads.
Innovation Solution
A lead frame design featuring a die pad and leads with integral inner leads, bent portions, and external connection terminals, where the leads are formed by a simple bending process that reduces stress and deformation, and the thickness and flatness of the leads are maintained through overlapping surfaces, allowing for accurate control and improved heat conductivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If wet etching is used to form anchor-shaped leads, then the leads can be thinned to achieve high-density packaging, but the manufacturing cost increases and processing speed decreases
Solution Approach 1:
The patent replaces the chemical wet etching process with a mechanical pressing process using a die to form the anchor shape in lead distal ends. This mechanical approach achieves the same lead thinning effect while dramatically improving processing speed and reducing manufacturing costs, as mechanical pressing can be performed rapidly in high-volume production compared to slow chemical etching processes.
2Productivity
If pressing process is used to form anchor shape in leads, then manufacturing cost decreases and processing speed increases, but large stress is applied to leads causing deformation
Solution Approach 1:
The pressing die is designed to apply stress locally only to the distal end portion of the leads where the anchor shape needs to be formed, rather than applying uniform stress across the entire lead structure. This localized pressing approach allows the lead to deform into the desired anchor shape at the distal end while the proximal portions and critical structural areas remain undeformed and maintain their original dimensions and flatness.
Solution Approach 2:
The pressing process is performed at a specific stage in the lead frame manufacturing sequence, after the leads have been formed but before final assembly and encapsulation. This timing allows the leads to be in a state where they can accommodate the localized pressing stress without permanent deformation, and the anchor shape is established before subsequent processing steps that might otherwise cause deformation.
3Productivity
If lead thickness is reduced for high-density packaging, then device density increases, but lead strength and heat conductivity may be compromised
Solution Approach 1:
The lead structure is designed with nested portions where the lead folds back on itself, creating overlapping sections. These nested portions effectively increase the cross-sectional area and thus the strength and heat conductivity of the lead without increasing its projected footprint. The multiple layers of metal in the nested regions provide enhanced mechanical strength and thermal pathways while maintaining the compact form factor required for high-density packaging.
Data Source
AI summary
A lead frame includes a die pad and a plurality of leads arranged around the die pad. Each of the leads includes an inner lead, a bent portion, and an external connection terminal. The inner lead includes a distal portion, adjacent to the die pad, and a connection end portion, located at an opposite end of the inner lead from the distal portion. The bent portion is connected to the connection end portion of the inner lead. The external connection terminal is connected by the bent portion to the connection end portion of the inner lead and located below the inner lead. The external connection terminal includes an upper surface that faces to and is parallel to a lower surface of the inner lead. The inner lead, the bent portion, and the external connection terminal are formed integrally in each of the leads.