Solder Bump Reliability Testing via Dedicated Test Structure
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Solution Overview
Problem
Existing methods for testing solder bump reliability in electronic devices are unreliable due to stress-induced delamination of the pad/substrate interface during probe testing, which does not accurately represent real-world handling stresses, and lead-free solders exhibit increased brittle failure modes, making it difficult to predict and prevent solder joint failures.
Innovation Solution
A test structure with pads extending under the solder mask and including all material layers contributing to intermetallic compound formation, plus an additional metallic layer, is used to simulate the mechanical attributes of the manufactured devices, allowing for enhanced prediction of solder bump failure modes and reliability testing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If probe testing is performed on solder bumps to predict failure, then reliability assessment is improved, but delamination of the pad/substrate interface occurs causing false test results
Solution Approach 1:
The patent creates a test structure that is a copy of the actual device structure, including identical pad, runner, and substrate configurations. This copy is used for testing instead of testing the actual device, allowing reliable failure prediction without damaging the real product. The test structure replicates all material layers and geometric features that contribute to solder joint behavior.
Solution Approach 2:
The testing process is segmented by separating the test function from the actual device. A dedicated test structure is created that contains only the necessary elements (pad, runner, substrate, solder bump) for reliability testing, while the actual device remains intact for its intended function. This segmentation allows independent optimization of the test structure for testing purposes.
2Object-affected harmful factors
If lead-free solder compositions are used to eliminate lead, then environmental compliance is improved, but brittle failure modes increase making failure prediction more difficult
Solution Approach 1:
The patent changes the physical and chemical parameters of the solder composition by using lead-free alloys with specific compositions (such as锡/银/铜 ratios). The test structure is designed to accommodate these parameter changes by providing a controlled environment where the brittle failure characteristics of lead-free solder can be properly characterized and measured.
Solution Approach 2:
The test structure is designed as a disposable, low-cost structure that can be intentionally failed during testing. Since the test structure is a copy rather than the actual device, it can be subjected to rigorous testing that would be too aggressive for the real product. The test structure absorbs the stress and failure risk, allowing reliable prediction without compromising the actual device.
3Measurement precision
If test structures use the same pad and runner configuration as manufactured devices, then testing accuracy is improved, but delamination occurs during testing
Solution Approach 1:
The test structure is prepared in advance with all the necessary material layers and geometric features that will be present in the actual device. The pad, runner, and substrate are configured exactly as they will be in production, allowing the solder bump to form and mature under the same conditions. This preliminary preparation ensures that the test structure accurately represents the actual device while being optimized for testing purposes.
Solution Approach 2:
The test structure serves as an intermediary between the testing process and the actual device. It provides a medium that can withstand the rigorous testing conditions while accurately representing the device's solder joint characteristics. The test structure absorbs the mechanical stress and delamination risk, allowing accurate failure prediction without directly compromising the actual device's integrity.
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 improves the reliability of solder bump failure prediction by accurately simulating real-world stresses and preventing delamination, enabling effective identification and remediation of problematic solder joints, even for lead-free solder compositions.
Implementation Method 1
the solder bumps are brought to a temperature exceeding their melting point... This heating process causes the formation of intermetallic compounds at the solder bump/pad interface
Implementation Method 2
a probe, 2 in FIG. 1, is traversed in direction 5 against solder bump 7... stress is applied in direction 25
Data Source
AI summary
Typical testing of solder joints, (e.g. joints at printed circuit board pads) has not proven totally predictive of the ultimate performance of such joints. It has been found that this lack of reliability is, at least in part, due to the tendency during testing for these pads to lose adhesion to, or delaminate from, the underlying substrate. In contrast, such occurrence is not typical of phenomena induced during typical device usage. To remove this source of unreliability, a test structure is made together with the manufacturing device lot. The same pad processing is used and the pad size is substantially enlarged in the test structure. The test structure is employed to predict performance of devices in the lot and then the lot is processed accordingly.