FMM28DSES

FAQFrequently Asked Questions

• What are the key design considerations when integrating the FMM28DSES into a dual-edge card slot application? The FMM28DSES is a 56-position dual-edge female connector with 28 positions per row, 0.156" pitch, and 0.062" card thickness specification. When designing the card slot, ensure the PCB or card edge is manufactured to exactly 0.062" thickness, as tolerance stack-up can cause insertion resistance issues or incomplete seating. The dual-edge configuration means signals are read simultaneously from both card surfaces; verify your backplane routing supports this parallel-read architecture and that signal integrity is maintained across both rows. The connector's full bellows contact design provides robust engagement, but initial insertion force may be higher than single-row designs—consider mechanical guides to prevent card skewing during insertion.
• Can the FMM28DSES handle the temperature extremes in aerospace or industrial equipment, and what design precautions are necessary? Yes, the FMM28DSES operates across -65°C to 200°C, making it suitable for aerospace, military, and high-temperature industrial environments. However, this wide temperature range requires careful thermal management during design. The gold contact finish with 30µin thickness provides corrosion resistance at temperature extremes, but thermal cycling stress can affect contact reliability over time. In applications with frequent thermal cycling, specify mechanical retention features to prevent connector creep or micro-motion that could degrade the contact interface. Additionally, ensure the PPS insulation material is validated for your specific thermal profile, as the connector's performance depends on maintaining dielectric strength across the full operating range. For mission-critical applications, accelerated thermal cycling testing should be performed on prototype assemblies.
• How does the FMM28DSES compare to single-row 28-position card edge connectors for applications where space is constrained? The FMM28DSES offers 56 total positions in a dual-edge (two-row) configuration versus a single-row 28-position connector. In terms of footprint density, the dual-edge design concentrates signal pathways in a smaller board area by utilizing both card surfaces, which is advantageous for compact backplane designs. However, the tradeoff is insertion complexity—dual-edge connectors require precise card alignment and have higher initial insertion forces due to simultaneous contact engagement on both rows. If your application can tolerate a longer single-edge connector footprint, switching to a single-row design may reduce assembly costs and mechanical stress on the card. For high-density applications like VME or CompactPCI derivatives, the FMM28DSES dual-edge configuration is more suitable; for simpler applications with relaxed space constraints, a single-row connector reduces design risk.
• What are the impedance and signal integrity implications of the 0.156" pitch spacing in the FMM28DSES for high-speed digital or RF applications? The 0.156" (3.96mm) pitch in the FMM28DSES is a legacy spacing common in industrial card-edge standards. For high-speed digital signals above 100 MHz or RF applications, this pitch becomes a constraint. The wider spacing eases mechanical design but limits the circuit density and can introduce crosstalk between adjacent signal lines if not carefully routed. Backplane PCB layout must incorporate controlled impedance traces, adequate ground planes, and may require length-matching or differential pair techniques to maintain signal integrity. At very high speeds (gigabit-class), consider termination schemes (AC or DC) to minimize reflections. The FMM28DSES itself does not specify impedance characteristics, so impedance control must be achieved through backplane and card design. For applications requiring sub-nanosecond timing margins, validate signal integrity with simulation and oscilloscope measurements during prototype validation.
• Is the FMM28DSES suitable as a drop-in replacement for older Sullins dual-edge connectors with equivalent pin counts, and what compatibility issues might arise? The FMM28DSES is part of the Sullins base series FMM28, which includes various configurations. When replacing an older dual-edge connector with the FMM28DSES, verify that the contact pitch (0.156"), card thickness (0.062"), row count (2), and position count (56 total) exactly match the original design. If the predecessor used a different contact material (e.g., phosphor bronze vs. the FMM28DSES's spinodal alloy), check for differences in contact force and insertion life—spinodal contacts generally provide better spring rate retention after mating cycles but may have different wear characteristics. Gold plating thickness is specified at 30µin; if the original used thinner plating (e.g., 10µin), ensure your contamination and corrosion environment does not exceed the durability of the thinner specification. The flange feature (side mount opening, unthreaded, 0.125" dia.) must also match; mismatches here prevent proper mounting. Test at least three prototype units with your actual card design before committing to production.
• What precautions should be taken when soldering the FMM28DSES eyelet terminations to avoid damage or reliability degradation? The FMM28DSES uses solder eyelet terminations, which require controlled wave-soldering or reflow processes. Excessive heat exposure can degrade the PPS insulation material—recommended reflow profiles should not exceed 260°C peak temperature for more than 10 seconds, and wave-solder immersion time should not exceed 5 seconds at 245°C. The gold-plated spinodal contacts can develop intermetallic layers if soldering temperatures are too high, degrading contact reliability. Pre-tin the eyelet pads lightly to reduce dwell time during soldering. Post-solder cleaning must remove all flux residues, particularly from the connector cavity and between contact bellows, as residual corrosive flux can cause leakage paths or galvanic corrosion over time. For applications in high-humidity environments, apply a conformal coating (acrylic or urethane) after assembly, but mask the mating face of the connector to preserve contact engagement characteristics.
• How many mating and de-mating cycles can the FMM28DSES withstand before contact wear becomes a concern? The FMM28DSES datasheet does not explicitly specify mating cycle life, but Sullins' spinodal contact material and full bellows design typically support 50–100 mating cycles under normal conditions (low-current signals, no erosion from arcing). In applications with frequent hot-swap or development environments where cards are repeatedly inserted and removed, contact wear accelerates. Each cycle slightly increases contact resistance as the gold plating wears and the bellows spring rate diminishes. For applications exceeding 20 mating cycles per year, consider mechanical wear testing on sample units or implement connector guides to reduce skew and side-load forces that accelerate wear. If your application requires hundreds of cycles, evaluate a higher-cycle-rated connector alternative or implement protective measures such as contact-wiping springs or redundant parallel contacts.
• What are the electrical performance limits of the FMM28DSES regarding current carrying capacity and voltage isolation between rows? The FMM28DSES does not specify current or voltage ratings in standard product documentation; these depend on circuit design, trace width, and creepage distances on the backplane and card. In typical industrial applications, each contact eyelet can safely carry 2–5 amperes at DC under normal thermal conditions, but this must be verified for your specific application by calculating I²R heating and ensuring backplane copper sizing supports the current density. For high-current applications (>10A per signal), use multiple contacts in parallel or dedicated power distribution contacts. Voltage isolation between the two rows is determined by the PPS insulation dielectric strength (typically 600–800V) and spacing on the backplane—creepage distance must meet IEC 60364 or equivalent standards for your target isolation voltage. In safety-critical or high-voltage applications, have a qualified design review performed to validate isolation adequacy.
• How does the RoHS3 compliance of the FMM28DSES affect long-term reliability in legacy or mixed-compliance assemblies? The FMM28DSES is RoHS3 compliant, meaning it contains no lead in the solder or plating. In legacy systems designed for RoHS-unrestricted (lead-bearing) components, substituting the FMM28DSES may introduce reliability risks if not carefully managed. Lead-free solder has a higher melting point (~220°C vs. 183°C for lead-based), requiring higher reflow temperatures that can stress the connector insulation if not controlled. Additionally, lead-free contacts can exhibit different contact resistance and migration characteristics compared to lead-bearing alternatives. If retrofitting older equipment, verify that your reflow or wave-solder process is validated for lead-free solder and that the connector's PPS insulation is qualified for the higher thermal exposure. For new designs, RoHS3 compliance of the FMM28DSES ensures regulatory compliance for EU market distribution and future-proofs the design, but do not assume drop-in compatibility with legacy lead-bearing backplanes without thermal and electrical re-validation.
• What environmental stress screening or acceptance testing protocol should be applied to FMM28DSES connectors in mission-critical applications? For aerospace, military, or medical applications, implement acceptance testing including visual inspection under 10× magnification for contact alignment and insulation defects, contact resistance measurement (target <50 mΩ per eyelet), and thermal cycling from -65°C to 200°C over 5–10 cycles to detect latent defects or solder joint anomalies. Conduct a sample lot test (per MIL-STD-1916 or equivalent) including insulation resistance (target >100 MΩ at 500V DC), dielectric withstand (1.5 kV AC for 1 second), and a subset of high-temperature operation (24–48 hours at 200°C) to validate component integrity. For connectors destined for high-vibration environments, perform vibration testing (MIL-STD-810 or equivalent) on assembled card-and-connector subassemblies to confirm no fretting corrosion or micro-motion wear occurs. Document all acceptance test results and establish traceability to part serial numbers, enabling rapid failure analysis if field issues emerge.
• Can the FMM28DSES be used in applications requiring hermetic or potted enclosures, and what design considerations apply? The FMM28DSES has a PPS insulation body, which is not inherently hermetic. In potted or encapsulated designs, the connector itself can be potted, but the mating face must remain accessible and protected from potting compound to preserve insertability. If the connector must be sealed or potted, confirm that the potting resin (epoxy, polyurethane, silicone) does not degrade PPS over time or interfere with contact engagement after curing. Spinodal contacts can absorb potting compounds in some cases, leading to contact resistance increases; pre-potting cleaning and drying are critical. For true hermetic applications (sealed against moisture or corrosive atmospheres), consider whether the FMM28DSES card-edge design is suitable—hermetic connectors often use different sealing technologies (e.g., glass-to-metal seals) not available in card-edge form factors. If hermeticity is required, consult Sullins technical support or evaluate alternative connector families specifically designed for hermetic service.
• How should the FMM28DSES be handled and stored to prevent contact oxidation or corrosion before assembly? The FMM28DSES features gold-plated spinodal contacts, which resist oxidation better than bare copper but are still susceptible to corrosion in aggressive environments. Storage should occur in controlled conditions: relative humidity <60%, temperature 15–25°C, and away from corrosive gases (sulfur, chlorine compounds). Connectors received in unsealed packaging should be stored in ESD-safe, moisture-barrier bags with desiccant packs. Do not expose the connector to thermal cycling during storage, as condensation can form on the contacts. If connectors are stored for >6 months, perform contact resistance verification before assembly to detect any oxidation buildup. Before soldering, do not clean gold-plated contacts with aggressive solvents; use IPA (isopropyl alcohol) only if necessary, and dry thoroughly with warm air to prevent water residue. For high-reliability applications, maintain a traceability log of storage conditions and shelf life to correlate any field failures to potentially degraded components.
• What is the mechanical mounting interface for the FMM28DSES, and are there standard backplane cutout or opening specifications? The FMM28DSES features a side-mount flange with an unthreaded 0.125" (3.18mm) diameter opening. The connector mounts to the edge of the backplane PCB via mechanical retention through this opening—typically using a bracket, standoff, or guide rail system rather than threaded fasteners. Standard VME, CompactPCI, or proprietary card-edge form factors define the exact mounting hole pattern and opening size; verify that your backplane design incorporates the correct flange clearance and retention scheme. The mounting must prevent lateral card drift during insertion, which occurs if tolerance stack-up between the connector flange, backplane opening, and card guide exceeds ±0.010". Mechanical engineers should specify backplane cutouts with tight tolerances (±0.005") to ensure reliable alignment. If custom mounting is required, consult the FMM28DSES dimensional drawings and verify that the connector flange does not interfere with adjacent components or cable routing.
• Are there recommended decoupling or EMI filtering strategies when using the FMM28DSES in mixed-signal or noisy industrial environments? The FMM28DSES itself does not integrate filtering or shielding; EMI control must be implemented at the backplane and card level. In noisy industrial environments, ground plane continuity is critical—ensure low-impedance ground paths from the FMM28DSES eyelets to the backplane ground return, minimizing loop area. For analog signals passing through the connector, implement local decoupling capacitors (0.1µF ceramic + 1–10µF electrolytic) placed within 0.5" of the connector eyelets on the card and backplane. Digital signal lines benefit from series damping resistors (10–100 Ω) to control ringing and crosstalk. If high-frequency switching (>10 MHz) is present, route power and ground signals through dedicated connector positions rather than mixing them with signal lines. Consider shield or guard traces on the backplane routing layer adjacent to signal layers to reduce capacitive coupling. For extreme EMI environments, add a shielded card cage or Faraday enclosure around the entire connector assembly, ensuring low-impedance bonding between shields and backplane ground.
• What is the typical cost and lead-time profile for the FMM28DSES, and are there volume-dependent availability constraints? The FMM28DSES is a mature, high-volume industrial connector with established supply chains through major distributors (e.g., Heilind, ScanSource, Arrow Electronics). Lead times are typically 2–4 weeks for standard quantities (100–500 units). Volume pricing is available for orders exceeding 1,000 units, with unit cost reductions of 20–40% compared to small-quantity pricing. Availability is generally reliable unless global semiconductor supply disruptions occur; however, Sullins may occasionally allocate stock during peak demand periods. If your application requires just-in-time delivery or rapid prototyping, verify stock availability with distributors before design lock. For large volume production (>10,000 units), consult Sullins directly regarding dedicated supply agreements or design-in support, as volume commitments may enable favorable pricing or extended lead-time commitments. Avoid sole-sourcing risk by maintaining a secondary connector option in your design or establishing a qualification agreement with a Sullins applications engineer.