Capillary Wire Bonding Without Lead Finger Tool Marks
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Solution Overview
Problem
Existing wire bonding techniques often result in tool marks on delicate lead fingers of printed circuit boards, which can lead to oxidation, contamination, and reduced bond strength due to contact between the capillary tip and the lead fingers during stitch bond formation.
Innovation Solution
A method and system for wire bonding that involves forming a ball bond on a semiconductor die and a stitch bond on a lead finger without direct contact between the capillary tip and the lead finger, using a capillary tool to feed the wire and determine optimal bonding parameters such as impact force, bonding force, ultrasonic energy levels, and temperature to prevent tool marks and enhance bond strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the capillary tip contacts the lead finger during stitch bond formation, then the bonding process is simpler and more direct, but tool marks are created on the lead finger surface causing oxidation and contamination
Solution Approach 1:
The patent introduces wire material as an intermediary between the capillary tip and the lead finger. The wire is fed through the capillary tip and makes contact with the lead finger instead of the capillary tip itself, thereby mediating the bonding process and preventing direct contact that would cause tool marks
Solution Approach 2:
The patent replaces the traditional mechanical contact-based bonding system with a system that uses ultrasonic energy and controlled wire feeding. The bonding is achieved through vibration and material deformation rather than direct mechanical pressure from the capillary tip, eliminating tool mark formation
2Force
If the capillary tip contacts the lead finger to form a stitch bond, then the bonding force is more direct and stronger, but the bond strength is reduced due to oxidation and contamination from tool marks
Solution Approach 1:
The wire material serves as a mediator that transfers the bonding force from the capillary tip to the lead finger without creating direct mechanical contact. This maintains the necessary bonding force while preventing the capillary tip from creating oxidizing tool marks on the lead finger surface
Solution Approach 2:
The patent applies preliminary ultrasonic vibration and controlled wire feeding before final bonding contact. This preliminary action prepares the wire and lead finger surfaces for bonding without creating tool marks, ensuring both sufficient bonding force and long-term bond strength
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution effectively prevents tool marks on lead fingers, resulting in stronger and more reliable stitch bonds, as demonstrated by increased wire material retention during pull tests, and can further strengthen the bond by contacting the stitch bond with the capillary tip after formation.
Implementation Method 1
Wire bonding is an electrical interconnection technique that uses thin wire and a combination of heat, pressure and/or ultrasonic energy. Wire bonding is a solid phase welding process
Implementation Method 2
moving the capillary tip towards a second location while the wire feeds out of the capillary tip
Implementation Method 3
Wire bonding is a solid phase welding process, where two metallic materials (e.g., wire and pad surface, or wire and PCB lead surface) are brought into intimate contact. Once the materials are in intimate contact, electron sharing or inter diffusion of atoms takes place
Data Source
AI summary
Apparatus and method for tool mark free stich bonding. In some embodiments, a method for wire bonding can include feeding a wire through a capillary tip and attaching a first end of the wire to a first location, thereby forming a ball bond. The method can further include moving the capillary tip towards a second location while the wire feeds out of the capillary tip. The method can further include attaching a second end of the wire to the second location while preventing contact between the capillary tip and the second location, thereby forming a stitch bond without a tool mark at the second location.