Semiconductor Wire Bonding via Inverted Ball Stitch
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Solution Overview
Problem
The existing wire bonding techniques for semiconductor chips, particularly downward wire bonding, result in increased costs due to larger electrode pads on thicker chips and potential bonding strength issues when materials differ, making it difficult to achieve compact, low-profile multichip packages with sufficient bonding strength.
Innovation Solution
A method involving mounting both semiconductor chips on a uniform substrate, forming a ball on the thicker chip's electrode pad, and bending the bonding wire into a V-shape or U-shape to increase the connection angle, allowing for second bonding on the thicker chip while maintaining a smaller electrode pad size, thus reducing costs and ensuring sufficient bonding strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If second bonding is performed on the thinner semiconductor chip (downward wire bonding), then the connection angle can be increased to maintain bonding strength, but the electrode pad on the thicker chip must be larger in size, leading to increased costs
Solution Approach 1:
The patent inverts the conventional downward wire bonding approach by performing second bonding on the thicker semiconductor chip instead of the thinner one. This inversion allows the bonding wire to achieve a sufficient connection angle (≥30°) with the thicker chip's electrode pad while keeping the electrode pad size manageable, thereby resolving the contradiction between bonding strength and pad size.
Solution Approach 2:
The patent changes the critical parameter of connection angle to be ≥30° by adjusting the bonding geometry and performing second bonding on the thicker chip. This parameter change enables sufficient bonding strength without requiring excessively large electrode pads, thus resolving the contradiction.
2Strength
If the electrode pad size on the thicker chip is increased to accommodate ball bonding, then bonding strength is improved, but manufacturing costs increase due to larger pad areas
Solution Approach 1:
By inverting the bonding approach and performing second bonding on the thicker chip with controlled electrode pad size, the patent achieves sufficient bonding strength without the need for excessively large pads, thereby reducing manufacturing costs associated with larger pad areas.
Solution Approach 2:
The patent employs a composite structure where the thicker semiconductor chip serves as the bonding substrate with optimized electrode pad characteristics. This composite approach allows achieving strong bonding interfaces without requiring uniformly large pad areas across the entire device, thus reducing overall manufacturing costs.
3Strength
If upward wire bonding is used to perform second bonding on the thicker chip, then the bonding wire must be routed to high positions or in trapezoidal loops, increasing costs and profile height
Solution Approach 1:
The patent inverts the conventional upward wire bonding approach by performing second bonding on the thicker chip in a manner that achieves sufficient connection angle without requiring complex high-position routing or trapezoidal loops. This simplifies the wire routing geometry and reduces device complexity while maintaining bonding 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
This approach reduces manufacturing costs by using less expensive thicker chips and enhances bonding strength by increasing the connection angle between the bonding wire and the thicker chip's electrode pad, even when materials differ.
Implementation Method 1
a tip of a bonding wire inserted in a capillary tool is first melted by discharge heating to form a ball
Implementation Method 2
the bonding wire is ball-bonded by ultrasonic welding while being pressed against an electrode pad on the semiconductor chip where first bonding is performed
Implementation Method 3
the bonding wire is stitch-bonded by ultrasonic welding while being pressed against the ball formed in advance on the electrode pad on the semiconductor chip where second bonding is performed. Therefore, the electrode pad on the semiconductor chip where second bonding is performed needs to be larger in size
Data Source
AI summary
A method for manufacturing a semiconductor device includes (i) a step of preparing a first semiconductor chip having a first electrode pad thereon and a second semiconductor chip having a second electrode pad thereon and larger in thickness than the first semiconductor chip, the second electrode pad being larger in size than the first electrode pad, (ii) a step of mounting the first semiconductor chip and the second semiconductor chip on the same planarized surface of a substrate having a uniform thickness, (iii) a step of bonding a ball formed by heating and melting a bonding wire to the second electrode pad, (iv) a step of first-bonding the bonding wire to the first electrode pad, and (v) a step of second-bonding the bonding wire to the ball.