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Extending Contactor Lifespans
December 31, 1969 |Estimated reading time: 4 minutes
By Nathan Verges, Antares Advanced Test Technologies
A semiconductor manufacturer needed a contactor to test a high-performance, high-pin-count CPU chip housed in a ceramic LGA package with gold-plated pads. Two customized contactor platings were tested, in combination with an on-site evaluation, to determine the most viable socket solution.
A global semiconductor manufacturer specializing in analog, digital, logic, and power-management technologies needed a contactor to efficiently test a high-performance, high-pin-count CPU chip housed in a ceramic land grid array (LGA) package with gold-plated pads. The coarse pads on the chip’s LGA package too quickly wore down the noble metals and plating of the previous vendor’s spring-pin contactor with standard gold plating. Two customized contactor platings - one a palladium/silver-based cobalt mix plating, the other with a carbon-based material - were tested to stand up to the LGA’s gold-plated pads. The sockets were used in combination with an on-site evaluation to determine the most viable testing solution.
The chipmaker needed a contactor that would enable, and not preclude, sustained, high-volume production runs. The coarse pads on the chip’s LGA package wore down the noble metals and plating of the previous vendor’s spring-pin contactor with standard gold plating after 3,000 compressions. The friction allowed oxide formation at the point of contact, resulting in a non-conductive exchange that prevented the chipmaker from eliciting viable test feeds.
The chipmaker’s senior staff engineer charged with overseeing all production at the facility was unable to maintain production of the CPU chips. The abbreviated lifespan of his contactors effectively paralyzed production. With this package, the contactor did not allow production to move at any sort of reasonable pace.
The senior engineer created a short-term solution as he contacted other vendors. He routinely stopped production on the CPU chip to clean the sockets, change out pins, and recalibrate the testing apparatus to extend the contactors’ lifespan before swapping them out altogether.
The semiconductor manufacturer’s engineer in charge of the situation ultimately installed sockets with palladium pins that didn’t last longer than the gold-plated spring pins. The density of palladium on the pins was relatively low, making the plating too weak to face the LGA package for extended runs.
Figure 1. Contactors in the socketing solution were able to withstand the rough and hard gold-plated package pads.
In the end, the ineffective contactors and the makeshift solution the senior engineer was compelled to implement idled large capital equipment investments at the chipmaker - including robotic handlers and testers at various stations - and resulted in low yields of the CPU chip.
The Solution
Two customized contactor platings that met production requirements and specifications for the ceramic LGA package with gold-plated pads were tested in a trial case. One of the sockets uses pins with a palladium/silver-based cobalt mix. The second socket solution uses pins with an experimental carbon-based material.
Engineers worked on-site with the chipmaker for eight weeks to qualify these solutions. Steps included analysis of the chipmaker’s statistical database to identify the testing parameters required by its CPU client, and testing the contactors to ensure they could accommodate the chipmaker’s production volume.
The engineers used the statistical database to extrapolate - based on a representative evaluation-stage sample size - the contactors’ anticipated failure rate during production and the appropriate order volume based on the chipmaker’s goals. Essentially, the engineers used the database and a predictive statistical methodology to ensure the contactors’ production-level reliability and readiness, avoiding makeshift solutions in the future.
Weekly follow-on visits were implemented between the socket provider and chipmaker’s senior engineer, for in-depth statistical database review and to modify socket solutions and platings as needed. This was done to allow the products to be used with multiple packages, handlers, and devices.
Both contactor solutions proved viable and cost-effective for testing with the LGA package’s gold-plated pads. Through the trial period and collaboration, the chipmaker was able to determine that the palladium/silver-based cobalt plating chemistry lasted longer in the given process.
The package’s gold-plated pads - which were characterized by their hard makeup and rough surface at the micro-structure level - quickly had worn down the conventional gold-plated contactors. This wear was causing them to fail. In contrast, the palladium/silver-based cobalt contactor was harder and less brittle than the gold-plated contactors and essentially was tough enough to penetrate the oxidization layer of the pads to improve the production lifecycle.
The chipmaker now is able to test the CPU chip in a ceramic LGA package with gold-plated pads in a cost-efficient manner without idling test stations, and is able to deliver significantly larger production yields for its client.
The chipmaker’s previous contactor solution lasted for 3,000 insertions. Through changing contactor plating and using the statistical evaluation with the socket provider, the new solution lasts 20,000 insertions. Uptimes of the CPU-focused test stations also increased, from about 35% to 99%.
Conclusion
When evaluating and tackling a production problem, the product is only part of the solution. On-site work with customers, reviewing data, evaluating systems, and critically examining results, can lead to a sustainable solution.
The global chipmaker required a new contactor makeup to withstand the harsh testing of a ceramic LGA package. Integrated product support enabled the contactor to be replaced; it also made it so the entire production process for this component was not at the mercy of one particular contactor.
This solution increased the number of insertions possible with a test socket at the facility, and also prevented capital equipment such as test stations, from sitting unused on the production floor, wasting possible uptime.
Nathan Verges, field applications engineer, Antares Advanced Test Technologies, may be contacted at 3350 Scott Blvd., Bldg. 58, Santa Clara, Calif. 95054; (214) 801-5960; nathan.verges@antares-att.com; www. antares-att.com.