ENGINEERING CHALLENGES
Key Engineering & Assembly Failure Modes
Solder Capillary Wicking
Molten solder rises inside internal threads due to surface tension during peak reflow.
PCB Internal Layer Damage from Press-Fitting
Mechanical broaching nuts apply high tonnages that damage inner microvias in multilayer HDI boards.
Torsional Solder Pad Tear-Out
High torque from automated electric screwdrivers can shear smooth solder pads from the board.
SMT Nut Mechanical Ratings & Torque Specifications
CUNECTRA STANDARD SPEC| Thread Spec | Recommended Pad Outer Ø | Stencil Thickness | Min Push-Out Force | Max Failure Torque | Recommended Tightening Torque |
|---|---|---|---|---|---|
| M2.0 x 0.4 | Ø 4.8 mm | 0.12 mm ~ 0.15 mm | ≥ 150 N | 1.2 N·m | 0.35 ~ 0.45 N·m |
| M2.5 x 0.45 | Ø 5.6 mm | 0.13 mm ~ 0.15 mm | ≥ 200 N | 1.9 N·m | 0.60 ~ 0.80 N·m |
| M3.0 x 0.5 | Ø 6.5 mm | 0.15 mm ~ 0.18 mm | ≥ 280 N | 3.2 N·m | 1.10 ~ 1.40 N·m |
| M4.0 x 0.7 | Ø 8.2 mm | 0.15 mm ~ 0.20 mm | ≥ 420 N | 6.5 N·m | 2.20 ~ 2.80 N·m |
| M5.0 x 0.8 | Ø 10.0 mm | 0.18 mm ~ 0.22 mm | ≥ 580 N | 11.0 N·m | 4.00 ~ 5.00 N·m |
DFM GUIDELINES
Design for Manufacturability Guidelines
01
Solder Stop Recess Step
0.25~0.40 mm counterbore cavity on fastener base.
Impact: Guarantees 100% thread clearance post reflow.
02
Knurled / Fluted Base
Radial micro-teeth machined onto bottom solder interface.
Impact: Increases torque retention by > 35%.
ENGINEERING FAQ
Frequently Asked Questions
Why choose SMT nuts over traditional broaching/press-fit PEM nuts?+
SMT nuts are placed by pick-and-place machines with zero mechanical insertion stress, allowing components on both board sides and protecting sensitive inner HDI layers.