Method and apparatus for manufacturing and probing printed circuit board test access point structures
View Patent ↗A test access point structure for accessing test points of a printed circuit board and method of fabrication thereof is presented. Each test access point structure is conductively connected to a trace at a test access point and above an exposed surface of the printed circuit board to be accessible for probing by a fixture probe. The test access point structure may be designed and manufactured to permit deformation of the test access point structure upon initial probing of the test access point structure with a fixture probe to ensure electrical contact between the fixture probe and the test access point structure.
1. An assembly, comprising:
a trace on a dielectric;
a solder mask characterized by a solder mask thickness and layered over said trace, said solder mask having a hole exposing a portion of said trace at a test access point location;
a solder bead soldered to said exposed portion of said trace in said hole of said solder mask, said solder bead projecting through said hole and having a solder bead thickness greater than said solder mask thickness, and
a fixture probe in contact with said solder bead.
2. An assembly in accordance with claim 1 , wherein:
said fixture probe is substantially flat.
3. An assembly in accordance with claim 1 , wherein said fixture probe compressively contacts said solder bead and deforms an upper surface thereof.
4. An assembly, comprising:
a trace printed along an x-y plane in an x-, y-, z-coordinate system of a dielectric, said trace generally characterized by a trace thickness along a z axis perpendicular to an x-y plane of said dielectric;
a solder mask layered over said trace;
a test access point structure conductively connected to said trace at a test access point, said test access point structure including a solder bead having a thickness greater than the solder mask thickness;
wherein said test access point structure projecting projects along a z axis in an x-, y-, z-coordinate system above an exposed surface of said solder mask on said printed circuit board to be accessible for electrical probing by an external device;
and a substantially smooth external device in compressive contact with said test access point structure.
5. An assembly in accordance with claim 4 , wherein said substantially smooth external device deforms an upper surface of said solder bead of said test access point structure from substantially round to substantially flat.
6. An assembly in accordance with claim 4 , wherein said substantially smooth external device deforms any contaminants on an upper surface of said solder bead of said test access point structure, and forms an electrical contact with said solder bead of said test access point structure.
7. An assembly in accordance with claim 4 , wherein said solder mask has an obround hole exposing said solder bead of said test access point structure.
8. An assembly in accordance with claim 7 , wherein said test access point structure comprises an oblong solder bead/bump running along an upper surface of said trace.