Adaptive Interposer Assembly for CTE Mismatch
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Solution Overview
Problem
Surface mount ceramic devices (SMDs) and printed wiring boards (PWBs) experience cracking due to mismatched coefficients of thermal expansion (CTE) during thermal cycling, leading to inefficiencies and increased costs in existing solutions such as SMD carriers and constrained-core PWBs.
Innovation Solution
An adaptive interposer assembly with a plate element and cavities filled with a high-compliance, high-melting-point solder material is placed between the SMD and PWB terminal pads, reducing CTE mismatch-induced loads and preventing substrate cracking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an SMD carrier with extended flat copper leads is used to reduce CTE mismatch, then substrate cracking is decreased, but the footprint on the PWB becomes relatively large
Solution Approach 1:
The interposer uses a localized approach by placing compliant material only in specific cavities at the solder joint locations rather than using an entire large-carrier structure. This concentrates the CTE compensation function where it is most needed (at the solder joints) while keeping the overall interposer footprint compact and matching the SMD device size.
Solution Approach 2:
The invention changes the material parameter by using compliant material with different mechanical properties (higher compliance) than traditional rigid carrier materials. This allows the interposer to accommodate CTE mismatch through material deformation rather than requiring a large structural design, thereby reducing the footprint while maintaining reliability.
2Reliability
If a constrained-core PWB with lower CTE is used to address substrate cracking, then thermal expansion mismatch is reduced, but manufacturing costs and delivery schedules increase
Solution Approach 1:
The interposer acts as an intermediary component between the SMD and PWB, introducing compliant material that mediates the thermal expansion mismatch. This approach is simpler to manufacture than constrained-core PWBs because it uses standard PWB materials and processes, adding only a thin interposer layer with cavity-filled compliant material rather than requiring complex core constraining structures.
Solution Approach 2:
The interposer creates a composite structure combining a rigid plate element (for structural support and electrical connectivity) with compliant material (for CTE accommodation). This composite approach achieves the thermal mismatch compensation function at lower cost and complexity compared to constrained-core PWB construction.
3Ease of manufacture
If traditional solder material is used between SMD and PWB, then assembly is simple, but the solder may deform or lose integrity during thermal cycling
Solution Approach 1:
The compliant material in the interposer cavities serves as beforehand cushioning for the solder joints. During thermal cycling, the compliant material deforms to absorb expansion/contraction stresses, protecting the solder material from excessive stress that would cause deformation or failure. This cushioning effect is built into the structure before thermal cycling occurs.
Solution Approach 2:
The invention changes the compliance parameter of the joint structure by introducing material with higher compliance between the SMD and PWB. This compliant material has a higher melting temperature and can withstand thermal cycling better than traditional solder alone, while the flush surfaces maintain proper solder joint geometry and electrical connectivity.
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 adaptive interposer assembly effectively minimizes substrate cracking and maintains efficient use of space by absorbing thermal expansion and contraction differences between SMDs and PWBs, while maintaining the solder's integrity during assembly and thermal cycling.
Implementation Method 1
substrate cracking of the alumina substrate due to SMD and PWB CTE mismatches can be experienced by the SMD. Such cracking can occur during thermal cycling
Implementation Method 2
The compliant material, which has a higher melting temperature than the first and second solder materials
Implementation Method 3
The compliant material, which has a higher melting temperature than the first and second solder materials
Data Source
Figure 1A~2B
Figure 3A~5B
Figure 6~7
AI summary
An adaptive interposer 60 is provided to be operably disposable between first and second solder materials 40, 50 of first and second electronic devices 20, 30, respectively. The adaptive interposer includes a plate element formed to define cavities and third solder material 72 disposable in the cavities to be electrically communicative with the first and second solder materials. The third solder material is more compliant and has a higher melting temperature than at least the second solder materials.