Dummy Pad Routing for Multi-Die Stack Wire Sweep Reduction
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Solution Overview
Problem
Conventional semiconductor package structures face challenges with long vertical wires that are prone to wire sweep, increasing the complexity and cost of the molding process and polishing.
Innovation Solution
A package structure with alternately stacked dies and strategically placed dummy pads, such as a second pad on the top die and third pads on other dies, reduces vertical wire lengths and risk of wire sweep, facilitating easier molding and reducing polishing costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If the distance from the top die to the second pad is increased to accommodate longer vertical wires, then the wire length increases, but the risk of wire sweep increases and molding complexity increases
Solution Approach 1:
The patent introduces dummy pads at different vertical levels (on the substrate and on intermediate dies) to create a three-dimensional wire routing path. Instead of extending the wire horizontally across the entire distance from top die to second pad, the wire can be routed vertically through intermediate dummy pads, effectively reducing the horizontal wire sweep distance while maintaining electrical connectivity.
Solution Approach 2:
Dummy pads act as intermediary connection points between the top die and the final second pad. These intermediate pads provide stopping points for wire bonding, allowing the wire to be bonded in segments rather than as one long continuous wire, thereby reducing wire sweep risk and enabling better process control.
2Reliability
If the cavity depth is increased to prevent wire sweep, then the wire sweep risk decreases, but the polishing cost increases
Solution Approach 1:
Dummy pads are strategically positioned at intermediate heights to serve as preliminary bonding points. This allows wire bonding to be completed in shorter segments before the molding process, eliminating the need for excessive cavity depth to accommodate long wires. The preliminary bonding action at dummy pads reduces the subsequent molding and polishing requirements.
3Length of moving object
If dummy pads are added on intermediate dies, then vertical wire length is reduced, but the device structure becomes more complex
Solution Approach 1:
The dummy pads serve multiple functions: they act as wire bonding termination points to reduce wire length, provide mechanical support structures, and serve as alignment references for subsequent bonding processes. By making these existing pad structures multi-functional, the patent reduces wire length without adding purely decorative or non-functional elements that would increase complexity.
Solution Approach 2:
The intermediate dies serve dual purposes: they provide structural support for the multi-die stack and simultaneously host dummy pads that facilitate wire bonding. The dies themselves contribute to the wire routing solution by providing their surfaces as bonding locations, rather than requiring separate dedicated wire routing structures.
Data Source
AI summary
Provided is a package structure including a substrate, N dies, N first pads, N vertical wires, and a second pad. The N dies are stacked alternatively on the substrate, so as to form a multi-die stack structure. The N dies include, from bottom to top, first to Nth dies, wherein N is an integer greater than 1. The first die is a bottom die, and the Nth die is a top die. The first pads are disposed on an active surface of the dies respectively. The vertical wires are disposed on the first pads respectively. The second pad is disposed on the top die.