Bond Finger Segmentation for Stack Package Signal Integrity
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Solution Overview
Problem
In semiconductor packaging, the varying lengths of bonding wires between stacked semiconductor chips can impair signal integrity due to length differences, leading to reduced signal quality and increased timing differences between reflection signals.
Innovation Solution
The use of a packaging substrate with bond fingers having distinct portions, where the second portion is closer to the chip stack than the first, allows for reduced length differences between bonding wires, improving signal integrity by minimizing signal reflection and increasing eye height in eye diagrams.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If bonding wires are used to connect stacked semiconductor chips to packaging substrate, then electrical connection between chips and substrate is achieved, but signal integrity deteriorates due to length differences between bonding wires
Solution Approach 1:
The bond finger is divided into multiple portions (first portion, second portion, third portion) along its length. Each portion serves a specific function: the first portion connects to lower chip bonding wires, the second portion (closer to chip stack) connects to upper chip bonding wires, and the third portion extends to the packaging substrate. This segmentation allows differential bonding wire lengths to connect to different portions, compensating for height variations and reducing length differences.
Solution Approach 2:
Different portions of the bond finger are positioned at different locations relative to the chip stack. The second portion is specifically positioned closer to the chip stack than the first portion, creating local variations in connection geometry. This local quality differentiation enables bonding wires of different lengths to achieve more equal effective lengths by connecting to optimally positioned portions.
2Adaptability or versatility
If bonding wires of different lengths are used for stacked chips, then all chips can be connected to substrate, but timing differences between reflection signals increase
Solution Approach 1:
The bond finger is segmented into multiple portions positioned at different distances from the chip stack. This allows bonding wires from chips at different heights in the stack to connect to different portions, equalizing their effective lengths and reducing timing differences in signal reflection.
Solution Approach 2:
Instead of varying bonding wire lengths in one dimension (vertical height), the solution introduces spatial variation in the horizontal plane by positioning bond finger portions at different lateral distances from the chip stack. This dimensional transformation compensates for height differences and equalizes signal path lengths.
Data Source
AI summary
There is provided a stack package. The stack package includes a packaging substrate and a chip stack disposed over the packaging substrate. The chip stack includes a second semiconductor chip that is stacked over a first semiconductor chip. The stack package further includes a first bonding wire connecting the first semiconductor chip to a first position of the packaging substrate and a second bonding wire connecting the second semiconductor chip to a second position of the packaging substrate. The second position of the packaging substrate may be closer to the chip stack than the first position of the packaging substrate.