Designing a PCB for an elastomeric connector requires a balance of mechanical precision and electrical reliability. Unlike traditional soldered connectors, elastomeric interconnects rely solely on controlled compression between the PCB pads and the conductive elements within the connector.
Proper pad layout, surface finish, and alignment are essential to achieve low contact resistance, long-term stability, and consistent performance.
1. Pad Layout and Geometry
Pad geometry directly influences contact pressure distribution and electrical performance.
Pads should be arranged in a linear array aligned with the connector’s compression axis, using consistent pitch and spacing as defined by the connector specification.
General recommendations:
- Pad shape: Rectangular pads oriented along the direction of compression.
- Pad dimensions: Width and length should provide ample contact area while maintaining sufficient isolation between adjacent pads.
- Pad finish: Use a flat, uniform plating to ensure even pressure during compression.
2. Surface Finish and Flatness
Because elastomeric connectors depend on pressure contact rather than solder joints, the surface finish and flatness of the PCB are critical.
We recommend ENIG or Hard Gold as the preferred finish due to its smooth topography, oxidation resistance, and long-term stability.
Other finishes such as HASL can introduce uneven surfaces that reduce effective contact area and increase contact resistance. Always verify planarity and surface cleanliness before assembly.
3. Soldermask Clearance — No Soldermask Between Pads
For elastomeric interfaces, soldermask should not be applied between contact pads.
Any raised mask edge can interfere with compression or cause uneven contact pressure across the pad array.
Best practices:
- Fully expose the contact copper across the entire pad array.
- Avoid narrow mask “slivers” between pads that can lift or flake during repeated compression.
- Define a single continuous mask opening that encompasses the pad row.
4. Via and Routing Considerations
Vias and plated through-holes beneath the elastomeric contact zone can create height variations or surface irregularities that compromise compression uniformity.
Guidelines:
- Do not place vias within or directly under contact pads.
- Maintain a minimum 0.35 mm clearance from pad edges to any via center.
- Route traces away from the contact area before transitioning to inner layers.
- If microvias are unavoidable, locate them just outside the compression region.
5. Mechanical Alignment and Mounting Holes
Mechanical alignment features ensure that the elastomeric connector seats consistently in position.
Accurate registration prevents lateral misalignment and guarantees uniform pressure distribution across all contacts.
Recommended practices:
- Include two or more alignment holes near the pad array for connector or fixture positioning.
- Maintain consistent hole-to-pad spacing across all design iterations.
- Provide a mechanical keepout area around the contact zone to prevent interference with components or hardware.
- Use compression stops or standoffs in the fixture or housing to control deflection and prevent over-compression of the elastomer.
6. Board Construction and Stiffness
The PCB surface under compression must remain flat and rigid.
For standard FR-4 boards, typical thicknesses between 1.0 and 1.6 mm offer adequate rigidity. For flexible or rigid-flex designs, a local stiffener should be applied beneath the contact area to maintain planarity. Avoid bending or twisting the PCB across the connector interface.
7. Electrical Performance and Grounding
Fine-pitch elastomeric connectors can support high-density or mixed-signal routing. To ensure signal integrity:
- Incorporate a continuous ground plane beneath the contact array when possible.
- For high-speed or sensitive signals, assign periodic ground pads to control impedance and reduce crosstalk.
- Maintain uniform compression pressure across all contacts to ensure consistent low contact resistance.
8. Testing and Validation
Reliable elastomeric interconnects depend on mechanical precision and surface integrity. Prior to production:
- Verify alignment and contact resistance using a dedicated compression fixture.
- Measure continuity across all contacts under the intended compression force.
- Perform environmental and life-cycle testing to confirm stable resistance and repeatable performance after multiple compression cycles.
9. Visual Aids in EDA Tools
PCB design tools can clearly illustrate the features of a well-prepared elastomeric interface:
- Mask-free contact pad region
- Defined mechanical hole locations
- Proper clearance from components and vias
- Pin 1 and orientation markings outside the compression zone
Summary
A well-designed PCB interface is the foundation of elastomeric connector reliability.
By eliminating soldermask between pads, ensuring flat ENIG contact surfaces, and incorporating precise mechanical alignment, designers can achieve consistent, low-resistance, solderless connections that perform reliably over time.
Z-Axis Connector Company provides engineering support and design consultation for integrating elastomeric connectors into new or existing systems. Our team helps customers optimize pad layouts, alignment features, and compression methods to ensure flawless electrical and mechanical performance from prototype to production.