The Essentra Components DLCBS3-3-19, a snap-lock nylon board support with a 3/16-inch mounting diameter, is a purely mechanical component designed for spacing and securing printed circuit boards (PCBs) within an enclosure. As such, it does not participate in any electrical circuit topology. However, its selection and integration directly impact the electrical performance of the system. The primary circuit design consideration is that this board support creates a low-impedance mechanical path between the PCB and the chassis or mounting surface. This path can inadvertently become an electrical path if not carefully managed. Therefore, the recommended "topology" is to treat the board support mounting hole as a potential ground reference point. For optimal performance, ensure that the mounting hole on the PCB is connected to the system ground plane, ideally through a low-inductance via array. This provides a defined, controlled electrical connection to the chassis, which is critical for both signal integrity and electromagnetic compatibility (EMC). Avoid leaving the mounting hole electrically floating, as this creates an uncontrolled parasitic antenna element.
For supporting passive components, the primary selection guideline is mechanical compatibility. The DLCBS3-3-19 has a 3/16-inch (0.1875-inch or 4.76mm) diameter mounting post. The PCB mounting hole must be drilled to a diameter that allows a secure snap-fit without excessive force. A nominal hole diameter of 0.187 inches (4.75mm) is recommended, with a tolerance of ±0.003 inches. The board support is made of nylon, which has a dielectric constant of approximately 3.5 to 4.0. While this is not a significant factor for low-frequency signals, at high frequencies, the nylon material can introduce a slight parasitic capacitance between the PCB and chassis. For RF or high-speed digital designs, consider using a board support with a lower dielectric constant material or ensure that the mounting hole is not placed near sensitive high-impedance nodes. For power supply decoupling capacitors placed near the mounting point, ensure the capacitor's voltage rating and dielectric type (e.g., X7R or C0G) are appropriate for the expected ripple and transients, as the mechanical stress from the snap-lock can, over time, affect ceramic capacitor reliability if they are placed directly under the mounting stress point.
PCB layout recommendations are crucial for reliable mechanical and electrical performance. The mounting hole pad must be designed as a non-solder-mask-defined (NSMD) pad with a copper annulus extending at least 0.010 inches (0.25mm) beyond the hole edge. Connect this pad to the ground plane using at least four thermal relief spokes or, preferably, a solid copper connection if the board support is intended as a direct chassis ground. For routing, avoid placing high-speed signal traces or sensitive analog traces directly under or within 0.050 inches (1.27mm) of the mounting hole on the same layer. This prevents crosstalk and noise coupling through the parasitic capacitance of the nylon post. On inner layers, ensure a solid ground plane surrounds the mounting hole area to provide a low-impedance return path. When using multiple board supports, space them evenly around the PCB perimeter, with a maximum spacing of 4 to 6 inches (100 to 150mm) to prevent board flexure. For boards with heavy components or in high-vibration environments, consider using a board support with a metal locking clip for increased retention force.
EMC/EMI considerations are dominated by the board support's role in grounding and shielding. The DLCBS3-3-19, when properly installed with the mounting hole connected to the ground plane, acts as a low-inductance ground strap to the chassis. This is beneficial for reducing common-mode emissions and improving immunity to external electric fields. However, the nylon material itself is an insulator. The primary EMC risk arises from a poor mechanical connection—if the snap lock is not fully seated, it can create a microphonic connection that generates intermittent ground loops. To mitigate this, ensure the chassis mounting surface is clean and conductive (if a ground connection is desired). For designs requiring a direct electrical bond to the chassis, consider using a metal-reinforced board support or adding a conductive gasket between the board and chassis at the mounting point. If the board support is intended to be electrically isolated (e.g., for a floating ground system), place a 0.1µF capacitor and a 1MΩ bleed resistor in parallel between the mounting hole and chassis ground to provide a defined AC path while preventing DC voltage buildup. Avoid routing any cables or wiring near board supports, as they can act as unintentional antennas if the support becomes a resonant structure at high frequencies.
Common design pitfalls include using an incorrect hole size, which can cause the snap-lock to fail or damage the PCB. A hole that is too tight will stress the nylon and can crack the board; a hole that is too loose will not retain the support. Always verify the hole diameter against the manufacturer's datasheet. Another pitfall is neglecting the thermal expansion coefficient mismatch between nylon (~80 µm/m°C) and FR4 (~14 µm/m°C). In temperature cycling environments, this can cause the board support to loosen over time. To avoid this, use a board support with a locking barb design or apply a small amount of thread-locking compound (non-conductive) to the post. A third pitfall is using board supports as the sole means of board retention in high-vibration applications. Always supplement with screws or other fasteners in at least two corners. Finally, avoid placing components directly under the board support's base, as the insertion force can crack ceramic capacitors or damage solder joints.
Prototyping tips and bench testing procedures should focus on mechanical integrity first. Before populating components, install the board supports into the chassis and press the PCB onto them. Verify that each support snaps cleanly and that the board is level and free of rocking. Use a torque gauge to measure the force required for insertion—it should be consistent across all supports. For electrical testing, connect a ground strap from the PCB's ground plane to the chassis and measure the resistance between the mounting hole and chassis; it should be less than 1 ohm if a ground connection is intended, or effectively infinite if isolation is required. Use a signal generator and oscilloscope to inject a 1MHz square wave into a nearby trace and observe any noise coupled to the chassis via the board support. For EMC pre-compliance, perform a simple radiated emissions scan with a near-field probe placed near each board support to identify any unintended radiation. During thermal cycling, test the board from -40°C to +85°C (or the expected range) and re-measure the mechanical retention force. Finally, for high-reliability designs, perform a vibration test per IEC 60068-2-6 to ensure the supports remain locked during operation. Document all measurements for the design review.
