Multi-Alloy Ball Grid Array Layout for Warpage-Prone Packages
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Solution Overview
Problem
Semiconductor packages face issues such as solder joint failures and head-in-pillow defects due to warpage of the circuit substrate, which can lead to intermittent connections and increased coplanarity of conductive interconnects.
Innovation Solution
A multi-alloy ball grid array is used, where two or more sets of solder balls made of different solder alloys are strategically arranged on the circuit substrate. The first plurality of solder balls with a higher melting point and stiffness coefficient is placed at high-stress areas, while the second plurality with a lower melting point and ductility is placed at low-stress areas.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single alloy ball grid array is used, then the manufacturing process is simple, but solder joint failures and head-in-pillow defects occur due to substrate warpage
Solution Approach 1:
The patent applies local quality by using different solder alloys at different locations on the substrate. High-stress areas (periphery) use solder balls with higher melting points and stiffness coefficients to resist warpage-induced stresses, while low-stress areas (center) use solder balls with lower melting points and higher ductility to accommodate thermal expansion. This location-specific material selection resolves the contradiction by improving reliability through targeted material properties without requiring a complete redesign of the entire ball grid array.
Solution Approach 2:
The patent employs composite materials by combining multiple solder alloys (e.g., SAC305, SAC105, SnBi8515) with different thermal and mechanical properties in a single ball grid array structure. This composite approach allows the system to simultaneously handle both high-stress and low-stress regions, improving overall solder joint reliability while managing the complexity through a systematic material distribution strategy.
2Reliability
If solder balls are placed at all locations, then electrical connectivity is comprehensive, but coplanarity increases due to warpage
Solution Approach 1:
The patent addresses coplanarity issues by applying local quality principles to the solder ball placement strategy. Rather than using a uniform approach, the patent selectively places different types of solder balls in different locations based on the local stress conditions. This localized differentiation allows the solder joints to better accommodate substrate warpage while maintaining overall coplanarity, thereby improving manufacturing precision without sacrificing electrical connectivity.
3Ease of manufacture
If uniform solder alloy is used throughout, then manufacturing is straightforward, but stress distribution during reflow is non-optimal
Solution Approach 1:
The patent resolves the contradiction between ease of manufacture and stress distribution by implementing local quality through a zoned solder alloy strategy. The manufacturing process remains relatively straightforward by using established reflow techniques, but the stress distribution is optimized by selecting specific solder alloys for specific zones based on finite element analysis of stress patterns. This approach maintains manufacturing feasibility while dramatically improving reliability during the reflow process.
Solution Approach 2:
The patent applies parameter changes by varying the material properties (melting point, stiffness coefficient, ductility) of the solder balls based on location. This parameter differentiation allows each region of the ball grid array to respond optimally to thermal and mechanical stresses during reflow, improving stress distribution without fundamentally changing the manufacturing process flow.
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 configuration reduces warpage of the circuit substrate and coplanarity of the solder balls, thereby minimizing failures such as solder joint failure, head-in-pillow defects, and hot shorting, and ensuring reliable electrical connections.
Implementation Method 1
two or more sets of solder balls made of different solder alloys are strategically arranged on the circuit substrate. The first plurality of solder balls with a higher melting point and stiffness coefficient is placed at high-stress areas
Implementation Method 2
This configuration reduces warpage of the circuit substrate and coplanarity of the solder balls, thereby minimizing failures such as solder joint failure
Data Source
AI summary
A semiconductor device assembly includes a circuit substrate comprising a first substrate surface and a second substrate surface arranged opposite to the first substrate surface; at least one die arranged on the first substrate surface; a package casing disposed over the first substrate surface, wherein the package casing encapsulates the at least one die and covers at least part of the first substrate surface; and a multi-alloy ball grid array coupled to the second substrate surface. The multi-alloy ball grid array includes a first plurality of solder balls made of a first solder alloy and a second plurality of solder balls made of a second solder alloy that is different from the first solder alloy.