Introduction: Most of the test probes are simple two-piece assemblies that provide a very direct path from the test pad to the tester interface. Since little electrical length or inductance is contributed by the test probe, the overall performance of the socket (fixture) can be enhanced by using a wireless construction. Design a fan-out pc board or translation board, which will carry the electrical signals from the test equipment to a pad pattern matching the device under test (DUT). The Micron test probes will provide a short, noise free connection between tester and DUT if this design concept is adopted. The i/o end of the test probe has a round (annular) contact are that is about one to one and a half mils in width (diameter equal to half the probe diameter). As the probe is compressed (before the test begins) it will try to rotate slightly. This action enhances the connection both at the tip end and i/o end of the probe. The figure inserted here shows an example of a BGA test socket. Selecting Probe Guide-Plate Material: Use a homogeneous, machinable plastic for the probe guide-plate. This will avoid problems which can arise when the drill strikes voids, fibers, soft spots in the plate. Consider using one of these trade marked materials or their chemical equivalents: Delrin, Ultum, Techtron, Peek, Vespel. In the simplest case, purchase or machine to a thickness equal to the probe spring length. Note when you select the probe that its Descriptive Model Name (DMN) includes the spring length and the plunger length. The DMN provides a quick reference to the probe diameter and probe guide-plate thickness, and plunger length. Drilling the Probe Guide-Plate: Avoid heating the plastic to its melting point. If your drill melts the plastic, then it may load down or may be pulled out of line by lateral forces. Keep the drill speed up and ‘peck’ the drill in and out of the hole to allow cooling and remove debris. We recommend a spindle speed of 50,000 to 120,000 rpm. Note that your drill surface cutting speed decreases as you move down to smaller drill sizes. Drill from one side only if for the best drilling accuracy and fixture performance. Drill the probe guide-hole to a depth equal to the spring (probe body) length. Counter drill the plunger guide-hole from the same side. If you elect to use the probe guide-plate as a mechanical stop for protecting the probes against over travel, then modify the probe guide-plate thickness specification. Rather than simply using the probe spring (body) length for the plate thickness, add to the thickness to limit the plunger travel. This protection can be accomplished other ways and the method used may depend upon your application. Installing Micron Probes: These probes can be the size of the 0,5 mm lead in a Pentel mechanical pencil or less than half that size depending upon the probe you select for your job. This may require some adjustment in perspective but it does not present any problems in handling, installing, inspecting, cleaning these probes. Use a pair of fine tipped tweezers that have not been distorted by other use. Cheap tweezers (you don’t have to spend $50 ea) can be used if you will modify the tip to create a sturdy, sharp tip. Stereo Zoom microscopes provide an excellent view of both the probe and the mounting hole in the socket (fixture). Try using a 20X version. Good lighting is critical. However, your microscope probably provides adequate lighting. Place the probe guide-block flat on the microscope work surface and install the test probes into the holes (generally with the tip down). Maintaining the Micron Probe Test Socket or Fixture: Clean daily by dipping a sponge ‘Q-tip’ into isopropyl alcohol and rolling it over the exposed probe tips. This will pick up some contaminants and debris whether airborne or generated by to tip-to-test surface action. Every 100,000 operations or so, clean the socket by placing it in a beaker of isopropyl alcohol and placing the beaker in an ultrasonic cleaner for about five minutes. Or, if you want to perform a more aggressive cleaning procedure, remove the test probes and clean both the probes and the unpopulated sockets (separately) using this procedure. Then dry the guide-plate and reinstall the probes. After the socket (fixture) has been reassembled. Test each probe. Press lightly on each probe and confirm that it exerts about the same force as the others and that it returns to the same height. This simple, functional test can detect probes that hang up in the guide-plate, that have bent plungers, or that have defective springs. Cleaning The Probe Guide-Plate: Clean the probe guide-block by placing it in a beaker of isopropyl alcohol, placing the beaker in an ultrasonic cleaner for approximately 5 minutes. Dry the guide-block and inspect for burrs and debris. The unique and proprietary design incorporated in the Micron Probe Series is covered by US and international patents.
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