How to build a quality probe card
Cantilever probe cards are used to probe microchips before dicing to determine whether the individual circuits meet their design specifications. Probe cards must enable reliable, repeatable, and consistent electrical contacts between the test system and the chip pads. Ensuring these probe cards are built with quality, accuracy and electrical integrity is vital to provide trustworthy and repeatable results.
From initial die layout through to completed probe card, the design, layout and build process needs to be seamless to ensure consistent quality. Here at Wentworth, with over 50 years’ experience, we have mastered the art of producing quality probe cards. Given the unique process required to build our quality products, it should be no surprise that probe card building solutions are not available “off the shelf”. We have used our experience in the design and development of probe stations to build specialised probe card manufacturing process equipment.
Probe card design and layout
Device layout and device files are available in many different formats. Our proprietary design to manufacture CAD/CAM software can accept a number of formats including CADF, CSV, XLS & TXT. We can also convert DWG, DXF, STP and Gerber formats for seamless use with this package.
The information required from our customer can be quite in-depth but the more detail provided, the better the manufacturing outcome. There are occasions when the only information available will be the pad co-ordinates, die layout and pad size so other parameters can be calculated or imported manually. When working with a new customer, we will build a default profile which provides us with some of the core information that is unlikely to change from device to device. This may include prober type, test environment and typical measurement parameters. The software also carries out some simple internal checks to the various parameters to identify errors in the information import such as pad size vs pitch etc.
All of the above information is used by the CAM system to provide the relevant files and detail to commence our manufacturing process. The software will also complement our experience in building probe cards by calculating the optimum probe material, probe tip shape, probe force & scrub as well as diameters and lengths.
Using typical industry standard algorithm to determine best-fit solutions, this can then be verified by our team prior to commencing manufacture.
Probe Card Manufacturing
Today’s probe card build processes are a far cry from the original building tools we developed back in the 1970s, which kick-started probe card building world-wide. These machines were little more than assembly fixtures to help the operators position the needles as close as possible to the centre of the pad and were very labour intensive when carrying P&A.
With today’s process, once the proposed layout has been accepted, our proprietary CAM system provides the probe card build-team with not only the relevant manufacturing drawing, but also:
• Photo-plot files
• Drill files for all probe layers
• Drawings and CNC files for the build fixture
• Drawings and CNC files for the ceramic rings
• Drawings and CNC files for PCB counter bore
• Tip radius parameters
• Probe card analyser files (API/Rudolph PRVX and ITC Probilt)
These are stored, ready to be called for each build stage of the probe card manufacturing process with the machining operations being fed direct to the tools.
Our mylar drilling station has also been developed using our expertise in producing high-accuracy stages for our probe stations. Being able to drill our probe card assembly tools to single digit µm accuracy, ensures excellent first-time alignment that requires the minimum of post-soldering manipulation. Further along the build process, our software will also analyse the required tip shape and generate the correct recipe to ensure the tips are shaped to the correct radius. Add to this our CNC milling systems ceramic ring and counter-bore applications, it provides all the programs and details required to build the card.
Quality
All our processes and internal developments are targeted to ensure that we can provide the quality our customers expect. Being able to remove human error in the input of data, is a key part of our ability to provide quality probe cards. Where manual input is required, having a degree of check and balances within the software package will highlight errors or parameter conflicts, helping to ensure we get it right – 1st time. The final piece of the process is to feed the analyser the correct file for final P&A inspection, ensuring a complete seamless design to delivery capability from Wentworth Laboratories.
