Angle Referenced Lead Frame Alignment Notch Design
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Solution Overview
Problem
Conventional lead frames for Quad Flat No Lead (QFN) packages face issues with bond wire crossings and shorts due to non-rotated IC chip mounting, requiring separate lead frames for different rotation angles, which increases manufacturing costs and variability.
Innovation Solution
An angle-referenced lead frame with alignment notches on the IC chip pad allows for precise mounting of IC chips at various rotation angles (0°, 30°, 45°, 60°, 90°) using a single lead frame, eliminating the need for multiple frames and reducing angle variation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If IC chip is mounted in non-rotated position on lead frame, then mounting process is simple, but bond wires cross and cause shorts
Solution Approach 1:
The lead frame introduces asymmetric features including a rotational reference marker and asymmetric pad layout. The reference marker provides a unique angular orientation, while the pads are positioned asymmetrically relative to the chip corners, enabling the mounting tool to automatically rotate the chip to the correct angle and prevent bond wire crossings without complex manual intervention
Solution Approach 2:
A rotational reference marker is introduced as an intermediary element between the lead frame and the mounting tool. This marker serves as a mediator that communicates the required rotation angle to the automated mounting equipment, enabling precise angular positioning of the chip while keeping the mounting process automated and simple
2Reliability
If IC chip is mounted in rotated position to avoid wire crossings, then bond wire shorts are prevented, but mounting angle precision decreases
Solution Approach 1:
The patent replaces manual mechanical alignment with an automated optical/electronic alignment system. The mounting tool uses the reference marker to automatically determine the correct rotation angle through detection systems (optical or electronic), eliminating manual measurement and improving angular precision to within specified tolerances
Solution Approach 2:
The reference marker is designed with specific geometric parameters (position, shape, orientation) that encode the required rotation angle. By changing the marker's parameters during design, the system can accommodate different chip orientations and package types, maintaining precision across various configurations
3Manufacturing precision
If separate lead frames are manufactured for different rotation angles, then mounting precision is improved, but manufacturing cost and complexity increase
Solution Approach 1:
The lead frame design achieves universality by incorporating a reference marker and asymmetric pad layout that work with multiple chip rotation angles (0°, 45°, 90°, 135°). A single lead frame design can accommodate different mounting orientations, eliminating the need for multiple specialized lead frame variants and reducing manufacturing complexity
Solution Approach 2:
The reference marker and asymmetric pad configuration are pre-designed into the lead frame before manufacturing. This preliminary encoding of angular information allows the automated mounting tool to determine the correct orientation without real-time complex calculations or multiple lead frame options, simplifying both lead frame design and mounting operations
Data Source
AI summary
A lead frame with an IC chip pad with an alignment notch. A method of mounting a packaged IC chip on a lead frame at a precise angle by aligning a corner of the packaged IC chip to an alignment notch on the lead frame.