Lead Frame Tie Bar Structure for Thermal Deformation Control
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Solution Overview
Problem
Existing lead frame structures face challenges in maintaining stability and flatness while minimizing thermal deformation and maximizing space for lead pads, as they are either overly stable with large tie bars or less stable with reduced tie bars.
Innovation Solution
A lead frame design featuring a die pad and tie bars with a multi-thickness thermal deformation mitigation structure, where the thickness varies from outer to inner portions, and tie bars have a larger contact area with the die pad and outer frame, reducing thermal deformation influence.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If four tie bars are used to support the lead frame, then stability and flatness are improved, but the available space for lead pads is reduced
Solution Approach 1:
The tie bars are segmented into multi-thickness structures with different thickness regions. The first thickness region provides flexibility while the second thickness region provides strength, allowing the tie bars to maintain stability with reduced material and smaller cross-section, thereby freeing up space for lead pads.
Solution Approach 2:
Different regions of the tie bars are assigned different thicknesses to perform different functions. The first thickness (thinner) region is positioned where flexibility is needed, while the second thickness (thicker) region is positioned where structural strength is needed. This local differentiation allows the tie bars to achieve both stability and space efficiency.
2Area of stationary object
If the number of tie bars is reduced to two, then the available space for lead pads is increased, but stability and flatness deteriorate
Solution Approach 1:
The thickness parameter of the tie bars is changed by introducing a multi-thickness structure. This allows the tie bars to provide enhanced structural support with optimized material distribution, compensating for the reduction in the number of tie bars from four to two, while maintaining both stability and maximizing space for lead pads.
Solution Approach 2:
The tie bars employ a composite thickness structure combining first and second thickness regions, creating a functionally graded structure that optimizes both mechanical support and space utilization. This composite approach allows two tie bars to perform the work of four conventional tie bars.
3Ease of manufacture
If uniform thickness is used in tie bars, then manufacturing is simplified, but thermal deformation resistance is reduced
Solution Approach 1:
The tie bars incorporate local quality variations through multi-thickness structures, where different thickness regions are positioned to resist thermal deformation in different areas. The thicker second thickness region provides enhanced resistance to thermal deformation while the thinner first thickness region maintains manufacturability through standard semi-etching processes.
Solution Approach 2:
The thickness parameter is varied along the length of the tie bars to optimize thermal deformation resistance. The transition from first thickness to second thickness is achieved through controlled manufacturing processes like semi-etching, maintaining ease of manufacture while significantly improving thermal deformation resistance through strategic parameter variation.
Data Source
AI summary
A lead frame includes: a die pad having a die disposing area; a plurality of lead pads located around the die pad; an outer frame, located at a periphery of the die pad and the lead pads; and at least two tie bars, respectively connected between the outer frame and two opposite sides of the die pad. At least one of the die pad and the tie bars includes a thermal deformation mitigation structure.