Turin (Italy)
May 03, 2024
Semiconductor Load Board Testing
How complete and automatic test of load boards can save you time and money
What is a semiconductor load board?
Semiconductor load boards, used for testing packaged ICs at the end of their manufacturing process, are the contact interface between the test head of the semiconductor test equipment and the pins of the devices under test. A load board is usually composed of a PCB that holds the test sockets (or contactors) on which the ICs under test are held, and that mounts on the test head.
The semiconductor load board construction must be free of defects, to ensure accurate and reliable verification of the IC integrity and performance.
Semiconductor load board defects
Like any electronic assembly, semiconductor load boards can also have construction defects that would compromise their performances when running on the test floor, affecting the results of the IC test.
Among the most common load board defects, we find:
- Short circuits
- Open pins
- Open tracks
- Defective socket-to-PCB connection
- Interrupted nets
- Defective socket contacts
- Weak components
- Weak relays
- Current leakage
To guarantee that a tester load board does not present any of these defects, its performances must be verified before their use in the production test floor, and confirmed with periodical checks to detect life-cycle failures that inevitably occur.
A single defect in these assemblies, if left undetected, will compromise the IC test results: you have no way to verify if a FAIL result is due to a real defect in the component under test, or to a defect in the load board itself.
How to test semiconductor load boards
Semiconductor load boards are often tested by running, on the same semiconductor tester they are going to be used on, a specific diagnostic procedure.
Although it is quite common, this practice presents several disadvantages:
- A high cost of test, since an expensive semiconductor tester (normally running 24 hours a day) is used, interrupting its productivity
- Long diagnostic test development
- Inadequate diagnostic capability: the functional test performed on the semiconductor tester is not able to detect all possible defects on a load board
- Long repair time: when a defect is detected, the tester is not able to provide a precise error message. The defective part is not identified, nor repair guidelines are provided: an expert test engineer has to make a deep, time-consuming analysis to repair the load board
- Hidden faults are not detected: defects that do not influence directly the functionality of the load board can create instability or malfunctioning in production
To overcome these limitations, and help saving time and money, it is recommended to use specific test methods and equipment to verify the load board performances, before their use on the IC test floor.
Semiconductor load board test equipment
SPEA flying probers can exhaustively test any type of load board, accurately verifying the correct functioning and parameter values for each component and net, so as to detect every process defect or component failure. In this way, they recognize faulty components, detect process defects (such as open pins or short circuits), identify components that perform out of their specifications and also “weak” components that are close to their end of life (e.g. relays).
The test is performed off-line, without needing to spend hours on the IC tester of destination, while releasing the load board testing from the required presence of an expert engineer. Precise diagnostic information is provided for every defect found, so that the expertise and time required to repair the load board are greatly reduced.
SPEA flying probers do not need any application-specific hardware: the tester automatically generates the test program in a few hours, starting from the CAD data of the load board. Even if CAD data is missing, the system is able to perform reverse engineering, useful to generate the test program or to replicate the load board itself.
Troubleshooting on defective semiconductor load boards
Even load boards that have performed well in the past can fall victim to a failure during their life cycle. In these cases, troubleshooting to determine the cause of the failure and repair the load board can be a time-consuming process for even the most experienced repair engineer.
SPEA flying probers can be profitably used not only to test fresh load boards after assembly. Their capability of accurate probing, their measurement accuracy and precise diagnostics build a great added value also for troubleshooting on defective load boards and performance verification after repair.
When a load board breaks down during its use on the semiconductor test equipment, SPEA flying probers simplify the repair process. It is enough to run the flying probe test program to get a precise diagnosis of the faulty part(s), off-line, reducing to minutes the downtime of the IC tester while minimizing the time to repair. Also the post-repair verification, before sending the load board back to the production floor, can be readily performed on the SPEA flying probers, getting a full test coverage.
Monitor the performance of semiconductor load boards
SPEA flying probers are not only able to detect load board failures, but also to monitor key parameters of critical components by applying real working conditions. This “stress test” is able, for example, to give indication not only about the correct working of a relay at the moment of test, but also about the degradation state of its contacts. Based on this information, it is possible to preventively replace those components that are likely about to break, thus drastically reducing breaks on field and consequent downtimes.
Build a semiconductor load board duplicate without CAD
In case load board documentation and schematics are missing, SPEA flying probers are able to automatically rebuild the board data: net list, electrical schematics, part list and CAD data are automatically generated. The result of this reverse engineering operation can be used to generate the flying probe test program to be run on the load board, or to make load board replicates.
Conclusions
As semiconductor ICs circuitries become increasingly complex and smaller in size, the need to accurately verify the tester load board and certify its good performances is of the utmost importance to ensure the test results reliability. However, testing the load boards using the same valuable tester used to verify the ICs is cost-demanding and inefficient, and can result ineffective in identifying certain defects.
The use of a flying probe tester to test semiconductor load boards can help saving time and money, offering the capability to detect all the possible defects, along the whole life cycle: from testing fresh load boards before their introduction in the test floor, to troubleshooting of defective load boards, periodic performance monitoring, reverse engineering.
