SMT Probe Selection
Spring probes designed for test centers of 0.050 inch or less are typically used for testing bare and loaded SMT boards. Special care is required when handling these very small probes and especially when inserting them in their receptacles. See Tools and Termination Instructions section.
SMT Pointing AccuracyThe pointing accuracy of a probe is defined as the radial play of the plunger tip measured from the centerline of the probe mounting hole. It is the result of a tolerance stack-up of the probe and receptacle assemblies.
Our SMT probes are manufactured to exacting tolerances to minimize radial play and ensure consistent, repeatable tip-to-target accuracy. The HPA-62 and HTP-62 series offer a receptacle with a double press ring to optimize perpendicularity and enhance pointing accuracy.
Pointing accuracy is significantly affected by a variety of other manufacturing tolerance factors. These include: angle of the probe mounting hole, probe plate warp, fixture-to-UUT registration, tooling hole/pin registration, etc.
Pointing accuracy specifications for our SMT probes are based solely on their mechanical limitations. The probes are designed to test SMT boards manufactured in accordance with testability guidelines established by the Surface Mount Technology Association (SMTA). SMTA studies recommend a minimum size of 0.035 inches for test pads to ensure probe-to-target contact. Testability guideline information is available from SMTA, in Edina, MN.
SMT Spring ForceSMT probes are offered in spring forces from 3.5 to 8 ounces. The lighter spring force should be used in densely-populated areas of a vacuum fixture to ensure proper vacuum actuation. High-force springs help provide better penetration of board contaminants, and are recommended for low-density applications.
SMT Receptacle InstallationSMT probe receptacles use single or double press rings for probe retention in the probe plate. Probe insertion should be done with care because the top of an SMT receptacle is more easily damaged than a 100 mil receptacle. Factory-authorized probe insertion tools are recommended.
Probe insertion can also be complicated if the probe plate hole is improperly drilled. The receptacle will accordion and jam a hole that is too small. or simply fall through a hole that is too large. Ideally, the press ring should collapse inside during insertion, creating a tight interference fit.
SMT Probe Plate Selection and Drilling TipsMaterials such as FR-11, phenolic, glass-filled polyester, sheet-molded compound (SMC), etc., can be used for fixture probe plates. Keep in mind that small hole drilling may require different drilling techniques than those used for standard test fixtures.
Most drilling experts recommend carbide drills and step-feed drilling to minimize drill breakage or "walking", regardless of the hole size. Opinions differ on the proper type of drill, flute length, RPM, feed rate and chip rate, so you may have to experiment to find the right combination for your application.
Entry and exit material, such as rigid aluminum foil, is highly recommended for drilling 0.050 inch and smaller test centers. Entry material helps pilot the drill bit to the correct position and keeps it perpendicular to the plate. Exit material cleans the drill bit at it withdraws from the hole.
SMT Receptacle Mounting HeightsThe height of an SMT probe can be extended by using probes with greater plunger travel, by mounting the receptacles at different heights, or by a combination of the two.
SMT Receptacle Termination StylesSMT receptacles are offered with crimp, solder, pre-terminated and FASTITE® terminations. See Receptacle Selection information in this section.
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