Virtual Reference Solder Joint Inspection via Laser Ultrasound
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Solution Overview
Problem
Current systems for inspecting solder joints in electronic devices are inefficient, unreliable, and often require a known good reference device, making them time-consuming and expensive, especially when detecting defects like cracked, misaligned, or missing solder bumps.
Innovation Solution
A non-contact, non-destructive inspection system using laser ultrasound and interferometric techniques to measure transient out-of-plane displacement responses of packaged electronic devices under pulsed laser excitation, enabling high throughput, resolution, and accuracy by correlating vibration responses to identify defects without a known good reference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If existing inspection systems use known good reference devices for comparison, then measurement precision can be improved, but inspection time and cost increase significantly
Solution Approach 1:
The patent creates a virtual reference model by collecting and processing vibration response data from multiple tested devices. Instead of requiring a physical known-good reference device, the system synthesizes a virtual reference that represents typical good device behavior, enabling rapid comparison without time-consuming reference device selection and validation
Solution Approach 2:
The system uses the tested devices themselves to generate the reference standard. By collecting vibration data from multiple devices and creating a virtual reference from this data, the inspection system becomes self-calibrating and does not require external reference standards, thereby eliminating the time and cost associated with obtaining and validating known-good references
2Reliability
If traditional contact inspection methods are used to identify reference devices, then reliability can be improved, but device complexity and cost increase
Solution Approach 1:
The patent replaces contact-based mechanical inspection methods with non-contact laser ultrasonic excitation and interferometric measurement. This substitution eliminates the need for physical contact with the devices, reducing mechanical complexity while maintaining or improving inspection reliability through optical measurement techniques
Solution Approach 2:
The system creates a virtual reference model that captures the essential characteristics of good devices without requiring physical reference devices. This virtual copy enables reliable defect detection while simplifying the overall system architecture by eliminating the need for maintaining physical reference standards
3Measurement precision
If high-resolution defect detection is implemented using conventional methods, then measurement precision improves, but productivity decreases due to time-consuming processes
Solution Approach 1:
The patent implements continuous, automated vibration data collection from multiple devices to build the virtual reference model. Once established, the virtual reference enables rapid sequential inspection of devices without interruption, maintaining high measurement precision while maximizing inspection throughput through uninterrupted processing
Solution Approach 2:
The system performs preliminary data collection and virtual reference creation during initial testing phases. This preliminary action establishes the reference standard in advance, allowing subsequent inspections to proceed rapidly with high precision without repeating the reference establishment process for each device
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 system provides efficient, reliable, and cost-effective detection of solder joint defects in electronic packages, improving manufacturing quality and reducing costs by using a virtual reference generated from averaged vibration data of multiple devices, allowing for dynamic updates and accurate identification of defective solder joints.
Implementation Method 1
a laser module to producing a pulsed laser beam used to excite at least one device containing a plurality of solder joints to vibrate the device
Implementation Method 2
to generate stress waves that induce vibrations
Implementation Method 3
an interferometer module disposed to sense vibration displacements created in the at least one device by the pulsed laser beam
Implementation Method 4
A vibrometer (e.g., a laser Doppler vibrometer) can be positioned to measure resulting out-of-plane displacement of the chip surface
Data Source
AI summary
Non-contact microelectronic device inspection systems and methods are discussed and provided. Some embodiments include a method of generating a virtual reference device (or chip). This approach uses a statistics to find devices in a sample set that are most similar and then averages their time domain signals to generate the virtual reference. Signals associated with the virtual reference can then be correlated with time domain signals obtained from the packages under inspection to obtain a quality signature. Defective and non-defective devices are separated by estimating a beta distribution that fits a quality signature histogram of inspected packages and determining a cutoff threshold for an acceptable quality signature. Other aspects, features, and embodiments are also claimed and described.