How to Choose a Spring Finger Contact

01 — What is the problem?

Spring finger contacts (also called BeCu fingers, ground clips, or battery contacts) are SMT or through-hole components used to create a reliable, vibration-tolerant electrical connection between a PCB and a metallic surface — typically a chassis, shield can, or battery. The selection looks simple but actually depends on several mechanical and electrical parameters: working height range, footprint, normal force, current capacity, and plating. A wrong choice leads to intermittent grounding, poor EMI performance, or even mechanical damage during assembly.

02 — Why does it happen?

• The available gap between PCB and chassis is rarely a fixed value — manufacturing tolerances stack up and require a contact with a sufficient compression range.
• Each spring finger family is optimized for a specific working height window (e.g. 1.5–3 mm, 3–6 mm, 6–10 mm) — picking the right family is the first step.
• Footprint and SMT pad layout must fit the available PCB area and be compatible with reflow soldering or pick-and-place machines.
• Normal force, plating (Au, Sn, Ni) and current rating drive the long-term contact resistance and EMI performance.

03 — Consequences

• Undersized compression range → contact loses pressure with tolerance stack-up, leading to intermittent grounding and EMI leakage.
• Oversized contact → excessive force on the PCB, risk of pad lift-off or housing deformation during closing.
• Wrong plating → oxidation over time, contact resistance increases and EMC performance degrades.
• Improper footprint → assembly defects, tombstoning, or unreliable solder joints.

04 — Common mistakes

• ✗Choosing a spring finger only based on its free height, without checking the recommended working range.
• ✗Ignoring the min/max compression — a spring finger must always be compressed within its elastic range, never bottomed out.
• ✗Forgetting to validate the footprint against the PCB layout and the pick-and-place nozzle compatibility.
• ✗Selecting tin-plated contacts for harsh or long-life environments where gold plating would prevent oxidation.
• ✗Not accounting for mechanical tolerances of the housing and PCB stack-up when defining the target compressed height.

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05 — Possible solutions

• ✓Step 1 — Measure the nominal gap between the PCB contact pad and the mating metal surface, then add the worst-case tolerance stack-up (min and max).
• ✓Step 2 — Select a spring finger family whose working height range fully covers your min/max compressed height, with margin on both ends.
• ✓Step 3 — Check the footprint and SMT compatibility (reusable pick-and-place cap, reel packaging, reflow profile).
• ✓Step 4 — Validate normal force and current rating against your application (grounding, signal return, battery contact).
• ✓Step 5 — Choose plating based on environment: gold for long-life, low-resistance, and harsh conditions; tin for cost-sensitive consumer applications.
• ✓Step 6 — Prototype and measure contact resistance under min and max compression to confirm reliable performance.

06 — Related topics

07 — Video