Diagonal Etched Lead Frame Connection Bar for Saw Blade Wear Reduction
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Solution Overview
Problem
Conventional lead frames used in semiconductor device assembly face issues with connection bar bending and lead shorting due to metal etching, which weakens the connection bar and causes saw blade wear, affecting the assembly process.
Innovation Solution
A lead frame design featuring connection bars with diagonal second portions that match the thickness of lead fingers, reducing bending and incorporating cavities at the first portions to minimize saw blade wear, while maintaining structural integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the connection bar is etched to be thinner than the leads, then it is easier to saw and causes less wear on the saw blade, but the connection bar becomes weakened and susceptible to bending
Solution Approach 1:
The connection bar is designed with non-uniform thickness: the first portion (at the lead finger connection) maintains full thickness for strength, while the second portion (between lead fingers) is etched to reduced thickness for easier sawing. This local differentiation resolves the contradiction by providing both structural integrity where needed and ease of manufacture where appropriate.
Solution Approach 2:
The connection bar is segmented into distinct portions with different thickness characteristics. The first portion connects to lead fingers with full thickness, while the second portion between lead fingers has reduced thickness. This segmentation allows the connection bar to simultaneously achieve strength at critical connection points and ease of sawing in non-critical areas.
2Strength
If the connection bar is made of metal, then it provides structural support, but it causes considerable wear on the saw blades used to singulate the assembled devices
Solution Approach 1:
The connection bar employs local quality by having different thicknesses in different portions. The first portion maintains full metal thickness for structural support at lead finger connections, while the second portion is etched to reduced thickness to minimize metal removal during sawing, thereby reducing blade wear while preserving necessary strength.
Solution Approach 2:
Instead of removing all metal from the connection bar (excessive action), the patent applies partial etching only to the second portion between lead fingers. This partial action is sufficient to reduce saw blade wear while maintaining adequate structural support through the first portion and the etched-but-present second portion.
3Productivity
If the connection bar is etched thinner, then less metal needs to be cut during separation, but the connection bar becomes susceptible to bending which moves the leads
Solution Approach 1:
The connection bar's local quality design ensures that the first portion at lead finger connections maintains full thickness for reliability and lead alignment, while the second portion between lead fingers is etched thinner to reduce separation effort and improve productivity. This localized differentiation resolves the contradiction between separation efficiency and lead alignment reliability.
Data Source
AI summary
A lead frame strip includes an array of lead frames. The lead frames each include a die pad and lead fingers that are spaced from the die pads and disposed along one or more sides of the die pads. The lead fingers have proximal ends near to the die pad and distal ends farther from the die pad. Connection bars extend between the lead frames. The lead fingers of adjacent lead frames extend from opposing sides of the connection bars. The connection bars have first portions where the lead fingers are connected thereto, and second portions between adjacent lead finger connections to the connection bar. The second portions are etched to form a bar that extends diagonally from a first one of the adjacent lead fingers connected thereto to a second one of the adjacent lead fingers connected thereto.