How do I select Base Material / Plating, Spring Force, and Tip Selection?
In the world of spring probes, choices abound when it comes to selecting materials and platings for plungers, barrels and springs. Choosing the right options can greatly impact yield, probe life and cleaning frequency.
BeCu is a popular choice for both plungers and barrels and has outstanding mechanical properties with high electrical conductivity. Steel is significantly harder and is typically used for plungers with aggressive tip styles. Nickel Silver is very resistant to corrosion and is well suited for barrels. Bronze has good wear resistance, cold formability and high electrical conductivity. Lastly, brass is a high quality material with high electrical conductivity and good wear resistance.
Choosing the right plating depends on the application and customer preference. Gold is widely used and provides excellent electrical performance and good corrosion resistance. To address lead free solder challenges, ECT has developed a proprietary plating material called LFRE which is approximately 5 times harder than gold. LFRE plated tips are much more durable and wear resistive than gold and have proven to last more than twice as long as gold plated probes. LFRE probes are also less susceptible to solder and material transfer and require less cleaning than gold plated probes.
Spring force selection is mainly dependent upon the application. It provides the required compliant force at the plunger tip and the contact force between the barrel and the plunger. Higher spring forces provide more effective penetration through contamination contact points, but leave heavier witness marks on the test point. Lower spring forces should be used where no witness marks are welcome or to prevent board flexing on higher pin count applications. Stainless steel must be used for springs when test temperatures exceed 100°C.
Most tip styles can be used for a variety of different applications. However, some test targets are better suited for unique tip styles. Some applications require a non-aggressive tip to be used on pads, such as radius, crown, or flat. These tips leave little to no witness marks on test pads. For through-hole vias ECT offers: blade, star, or pyramid tip styles. These are well suited for contact through the outer ring of the via surface. Over time solder builds up oxide layers, therefore medium to very aggressive tips like the serrated, crown, blade, pyramid and point are used. Posts, pins or screws are more unpredictable and therefore more challenging. For these applications, tip styles like the cup, serrated and crown are best suited. Other applications may require more unique tip styles depending on test target material, size, shape, access and cleanliness. With over 50 years of making high quality spring probes, ECT has developed a vast library of probe options for all your testing needs.
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