Substrates are used to enable a connection between a semiconductor and a printed circuit board. A characteristic test panels consists of about 50 – 100 single substrates and has a size of approx. 250 mm x 80 mm. For electrical testing it is necessary to contact all end points of the product. Each substrate has about 1000 – 2000 test points. So on one product about 100,000 pads need to be contacted. For testing substrates on the semiconductor side, structures down to 10 µm have to be reliably contacted.
To meet this challenge the system deploys four freely moveable test heads and achieves a test rate of 100 measurements per second. The test heads contact the test product from above and execute a capacitance measurement against a vacuum table. The capacitance result indicates opens and shorts in the substrates.
Prior to electrical test, an optical alignment of the test sample correlates the shrinkage and offset of the finished product with the testing data and adjusts automatically. A 5 Megapixel color camera with a resolution of 1.2 µm ensures positioning accuracy of ±1.5 µm.
The system works with a micro needle. The contacting pressure of this micro needle can be adjusted from 0.3 g up to 2.5 g to ensure best test yield and repeatability without damaging the contact pads. The maximum test area of the substrate tester is 310 mm x 300 mm (12.2” x 11.8”).
