A
test probe consists of an elongated screw
machine contact biased by a
helical spring and mounted in a through hole of a non-conductive substrate. One end of the contact includes a crown for engaging a
solder ball lead of an IC
package, and the contact includes an intermediate collar which maintains the contact within the through hole. The
helical spring is disposed about the contact, with one end thereof engaging the lower end of the collar. The other end of the
helical spring has contiguous coils and is of a reduced
diameter so as to extend beyond the lower end of the non-conductive substrate to make electrical contact with a
printed circuit board. When the
test probe is compressed between the IC
package and the
printed circuit board, the inherent twisting of the helical spring causes the contact to tilt and make electrical contact with the contiguous coils, thereby establishing a direct electrical path between the IC
package and the
printed circuit board, with minimum resistance and minimum
inductance. In an alternate embodiment, each probe is disposed within a
dielectric housing which, in turn, is disposed in a through hole in a conductive substrate to effectively shield the probe from electrical interference.