Wire Bonding Method for Low-Profile Loop Formation
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Solution Overview
Problem
Conventional wire-bonding methods face challenges in reducing the height of the wire loop while maintaining wire strength, often resulting in damage to the wire near the first bonding point and difficulty in forming low-profile loops due to frictional forces and structural weaknesses.
Innovation Solution
A wire-bonding method involving a capillary that performs sequential movements, including vertical and oblique downward motions with arc-wise trajectories, to form kinked portions in the wire, reducing the height of the wire loop while preventing strength degradation by minimizing tensile loads and frictional damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If the capillary moves horizontally toward the second bonding point after bonding to the first bonding point, then the wire loop height is reduced, but the wire neck portion is damaged due to friction between the capillary and the thin metal wire
Solution Approach 1:
The capillary moves along an arc-shaped trajectory instead of a straight horizontal path. The movement consists of an upward arc motion from the first bonding point to an apex position, followed by a downward arc motion to the second bonding point. This curved path reduces direct frictional contact between the capillary and wire neck, preventing wire damage while achieving low wire loop height.
Solution Approach 2:
The capillary movement is extended from a two-dimensional horizontal plane to a three-dimensional space by incorporating vertical upward and downward motions. The capillary rises to an apex position above both bonding points and then descends to the second bonding point, creating a spatial arc trajectory that minimizes frictional damage to the wire while controlling loop height.
2Length of stationary object
If the capillary moves upward to a position several times higher than the desired arch height and then moves downward in an arc-wise manner, then the wire loop height is reduced to about 100 μm, but the wire strength decreases due to tensile load and frictional force
Solution Approach 1:
The invention optimizes the arc movement parameters, specifically setting the apex position at a controlled height above the bonding points and adjusting the arc radius and trajectory. By carefully controlling these movement parameters, the wire loop height is reduced to about 100 μm while minimizing the tensile load and frictional force applied to the wire, thereby preventing wire strength degradation.
3Length of stationary object
If the capillary moves downward by a distance shorter than the rising distance to press down the wire, then the wire loop height is reduced, but the wire is damaged due to excessive frictional force and tensile load
Solution Approach 1:
The capillary employs arc-shaped upward and downward movements instead of direct vertical pressing. The upward arc motion from the first bonding point to the apex and the subsequent downward arc motion to the second bonding point distribute the mechanical stress more evenly, reducing both frictional force and tensile load on the wire while achieving the desired wire loop height reduction.
Data Source
AI summary
Wire bonding method for reducing height of a wire loop in a semiconductor device, including a first bonding step of bonding an initial ball formed at a tip end of a wire onto a first bonding point using a capillary, thereby forming a pressure-bonded ball; a wire pushing step of pushing the wire obliquely downward toward the second bonding point at a plurality of positions by repeating a sequential movement for a plurality of times, the sequential movement including moving of the capillary substantially vertically upward and then obliquely downward toward the second bonding point by a distance shorter than a rising distance that the capillary has moved upward; and a second bonding step of moving the capillary upward and then toward the second bonding point, and bonding the wire onto the second bonding point by pressure-bonding.