PCB Tail Specific Information
Key considerations for engineers integrating D38999 connectors onto PCBs:
PCB Tail Dimensions and Plating
Ensure the connector's PCB tail specifications align with PCB design requirements:
- Tail Lengths: Standard tail lengths correspond to common PCB thicknesses (e.g., 0.093" or 2.36 mm). Tail lengths can range from 0.094" to 0.500" (2.38 mm to 12.70 mm).
- Tail Diameters: Vary according to contact size:
- Size 22D: ~0.018" (0.46 mm)
- Size 20: ~0.025" (0.64 mm)
- Size 16: ~0.040" (1.02 mm)
- Size 12: ~0.072" (1.83 mm)
- Plating Materials: Contact tails are typically plated with 50 microinches of gold over nickel per ASTM B488 standards to ensure excellent solderability and corrosion resistance.
PCB Footprint Design
Design considerations to ensure reliable connections and mechanical stability:
- Drill Hole Sizes: Use recommended drill sizes with appropriate plating allowances. For example, for a size 22D tail (~0.018" diameter), a hole size of 0.022" to 0.024" (0.56 mm to 0.61 mm) is typical.
- Annular Ring: Maintain sufficient annular ring (pad size) around the plated through-hole to ensure mechanical strength and solder fillet formation.
- Pad Layout: Follow IPC-2221 standards for land pattern design, considering factors like pad size, spacing, and thermal relief connections.
- Signal Integrity: For high-speed or differential signals, maintain controlled impedance by carefully designing trace widths and spacing according to your PCB stack-up.
- 3D Modeling: Use 3D models of the connector to verify mechanical fit and clearance in the final assembly.
Soldering Recommendations for PCB Tail Connectors
Guidelines to ensure reliable solder joints and avoid damage:
- Solder Alloy: Select appropriate solder alloy (e.g., SAC305 for lead-free processes) compatible with connector materials.
- Flux Type: Use flux compatible with both the solder alloy and connector plating. No-clean fluxes are preferable to avoid cleaning steps.
- Soldering Methods:
- Wave Soldering: Ensure the connector can withstand the thermal profile. Provide proper thermal shielding to prevent solder bridging.
- Selective Soldering: Offers precise control for connectors with tight pin spacing or mixed technology boards.
- Preheating: Preheat assemblies to reduce thermal shock and improve solder flow, minimizing the risk of thermal damage.
- Process Controls: Monitor solder temperature, conveyor speed, and other parameters to maintain consistent solder quality.
Mechanical Support and Reinforcement
Enhancing mechanical stability of the connector on the PCB:
- Mounting Hardware: Use threaded inserts or through-hole screws to secure the connector to the PCB or chassis, reducing stress on solder joints.
- Board Reinforcement: In high-stress environments, consider reinforcing the PCB area around the connector with additional layers or stiffer materials.
- Potting and Encapsulation: Apply potting compounds to encapsulate the connector area, providing environmental protection and mechanical support.
Environmental and Operating Conditions
Factors affecting the performance and reliability of PCB-mounted connectors:
- Temperature Cycling: Design for thermal expansion compatibility between the connector, solder joints, and PCB materials to prevent fatigue cracking.
- Moisture and Contaminants: Implement conformal coatings or sealing methods to protect against moisture ingress and contaminants, especially in humid environments.
- Vibration and Shock: Ensure that mechanical reinforcement is adequate to withstand specified levels of vibration and shock per MIL-STD-810 standards.
Electrical Performance Considerations
Ensuring the connector meets the electrical requirements of the application:
- Contact Resistance: Low and consistent contact resistance is critical, particularly for power contacts. Verify specifications provided by the manufacturer.
- Current Carrying Capacity: De-rate current capacity based on PCB thermal characteristics and environmental conditions.
- Signal Integrity: For high-speed signals, minimize impedance discontinuities and crosstalk by careful PCB layout and connector selection.
- EMI/RFI Shielding: Use connectors with conductive backshells and proper grounding to shield sensitive signals from electromagnetic interference.
Standards and Compliance
Adherence to relevant industry standards ensures reliability and interoperability:
- MIL-DTL-38999: Ensure connectors comply with this military specification for performance and environmental resistance.
- IPC Standards: Follow IPC-A-610 for acceptability of electronic assemblies and IPC-J-STD-001 for soldering processes.
- RoHS and REACH Compliance: Verify material compositions to ensure compliance with environmental regulations, if required by the application.
Ordering and Part Numbering
D38999 connectors have complex part numbering systems that specify their configuration:
- Shell Style: Indicates the mounting style and coupling mechanism (e.g., wall mount, jam nut).
- Service Class: Defines materials and finishes for corrosion resistance and conductivity.
- Contact Style: Specifies contact type (e.g., solder, crimp, PCB tail) and whether contacts are included.
- Insert Arrangement: Denotes the contact layout within the connector per standardized patterns.
- Keying Position: Identifies the rotational position of keying features to prevent mismating.
Consult the manufacturer's catalog or technical support for assistance in building the correct part number for your application.