LTCC MmWave Antenna-Filter Module for CTE Mismatch Reliability
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Integrated low temperature co-fired (LTCC) antenna-filter array modules for mmWave 5G advanced antenna systems face reliability issues due to mismatched Coefficients of Thermal Expansion (CTE) between the antenna-filter array and the radio PCB, leading to solder ball cracking under thermal stress, which is exacerbated by larger module dimensions and cannot be effectively addressed by existing solutions like underfill techniques, solder-coated polymer balls, or interposer boards.
Innovation Solution
The method involves identifying a maximum size for LTCC antenna-filter units that do not cause reliability issues by soldering an LTCC tile with multiple antenna elements onto a module PCB with a CTE close to the radio PCB, then cutting the tile into smaller reliability-issue-free units, ensuring the module PCB's CTE matches or closely matches the radio PCB's, thereby reducing thermal stress and maintaining alignment for improved beamforming performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the dimension of the LTCC antenna-filter array is increased to meet engineering requirements (avoiding grating lobes and reducing mutual coupling), then the antenna performance is improved, but the thermal stress on solder balls increases due to larger span and CTE mismatch, leading to solder ball cracking and module failure
Solution Approach 1:
The patent introduces an interposer board that segments the thermal expansion path between the LTCC antenna-filter array and the radio PCB. The interposer board acts as an independent intermediate layer, dividing the original single-step thermal stress transmission into two separate interfaces, thereby reducing the cumulative thermal stress on solder balls while allowing the antenna array to maintain its required larger dimensions for optimal performance
2Reliability
If the CTE difference between LTCC antenna-filter array and radio PCB is reduced by selecting matching materials, then thermal stress is reduced, but adaptability is lost since standard PCB materials (Megatron-6, FR4) cannot be used
Solution Approach 1:
The interposer board serves as a mediator between the LTCC antenna-filter array and the radio PCB. It has a CTE that is intermediate between LTCC and standard PCB materials, creating two smaller CTE mismatches instead of one large mismatch. This allows the system to maintain reliability by reducing thermal stress while preserving adaptability to use widely available standard PCB materials like Megatron-6 and FR4
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 enhances the reliability and beamforming performance of the LTCC antenna-filter array module by eliminating thermal mismatch and misalignment issues, while being cost-effective and compatible with existing radio PCBs.
Implementation Method 1
module PCB having a CTE that is close to or equal to the CTE of the radio PCB, the closer the two CTEs, the greater the reliability of the antenna-filter array module
Data Source
AI summary
An antenna-filter array module and method of manufacturing an antenna-filter array module are provided. One method of manufacturing includes bonding a low temperature co-fired ceramic, LTCC, tile having a plurality of antennas and corresponding filters to a first side of the module PCB via a first set of solder balls, a coefficient of thermal expansion, CTE, of the module PCB being within a predetermined amount of a CTE of the radio PCB. The method further includes cutting the LTCC tile into a plurality of reliability units after the bonding, each reliability unit having a size that is less than a predetermined largest reliable size.