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Insights on Machined Pin and Socket Assemblies

Manually placing fields of discrete pins upon a printed circuit board is a poor production PCB assembly strategy. This action is not only tedious and prone to errors but extremely cost-ineffective too.

Vertically unstable pins tilt, creating harmful soldering rework. Misaligned mating connector pins bend, or worse, break.

Increase pin to PCB retention and improve vertical alignment by packaging discrete pins into a molded or machined insulator.

For very low socket profiles, consider using carrier assemblies. Socket carriers are assemblies featuring a removable insulator. After placing the carrier assembly upon a PCB and soldering, the carrier insulator is lifted off. Carriers not only place low-profile sockets but without an insulator obstructing the view, solder inspection becomes easy.

Floating pin technology is a unique approach to addressing the challenges of SMT pin coplanarity. Floating pin connectors contain pins that independently travel vertically (“float”) inside the molded core cavity, finding their height on the peaks and valleys of uneven solder paste.

Insulator Design Tips:
COTs products are typically in standard industry grid configurations of .100”, 2mm, .070”, .050”, 1mm, and possibly 0,8mm.

Custom footprint pin patterns are molded or machined (milling and drilling) using plastic or FR-4 materials.

When designing a surface mount connector, consider the factors affecting pin coplanarity. Press-fit pins will induce stresses into the insulator encouraging insulator warpage.

Designing a pick and place surface directly into a molded insulator will product costs and improve PCB assembly rates by eliminating the need for a separate pick and place cap.

Always design connectors on tape and reel for high-speed, production. If the connector must sit in the tape pocket in its indexed orientation to the PCB.

Machined pins are typically press-fit assembled into thermoplastic insulators. A knurl press-fit feature prevents torquing forces from pin spinning.

Phosphor bronze alloy is a superior choice for right-angle pins. It has a higher yield strength than brass. Connector pins slightly bend during handling. Bent brass alloy pin tails become very brittle at the bend and will crack if re-straightened.

For insulators, incorporating counterbore pin cores allows pin shoulders to not only recess flush but stay vertically straight.

For horizontal-mount connectors, the pin centerline is usually the mid-point of the insulator thickness. This is the pin centerline offset off the PCB. Check the mating connector. It must have the same pin centerline to ensure connector mating is possible.

Incorporating alignment pins in the diagonal corner locations of an insulator serves many purposes. For a surface mount connector, alignment pins center the connector pins to their respective SMT pad pattern. Alignment pins provide mechanical strength against pushing engagement forces and protect surface mount solder joints.

Regarding Insulator Construction:
Do not expose male connector pins to side-loading forces. Recess or shroud male pins for protection.

Pin insulators are machined, injection-molded thermoplastic, molded thermosets, and even 3D printed.

Heat creates a branding iron effect inside a molded or machined hole.

This heat causes material inside the hole to burn off. TCE, the thermal coefficient of expansion, affects material expansion and contraction. TCE influences and can compromises pin retention inside an insulator.
Insulators should have sufficient glass content to withstand a typical RoHs soldering process temperatures up to 260C.

Thermoplastics are recyclable and can be re-ground. Thermosets are not recyclable and burn if re-melted.

Loose pins are press-fit into thermoplastic insulators. For thermoset insulators, pins are fixtured as the thermoset is poured into the mold.

Loose pins are typically press-fit into thermoplastic insulators. For thermoset insulators, pins are fixtured, and the thermoset compound fills the mold. Thermoset insulators mold around the part.

Regarding Pin Design:
LIFs are low insertion force sockets. A ZIF is a zero insertion force socket. For high pin counts, a ZIF socket is much easier to use. An advantage a LIF socket has over a ZIF socket is the board space required. The LIF socket will require much less board space, as the ZIF socket is mechanical and needs room for a lever.

When designing large socket arrays, make sure to use socket receptacles containing low-insertion force clips. Look at the accumulative insertion and withdrawal forces.

Whenever the opportunity presents itself, make your pin design bi-directional, this improves production assembly rates.

If your pin design is not bi-directional, then you must incorporate indexing features to make the pin load only in one direction into the insulator. If you do not, you will have tremendous product assembly difficulties.

Incorporate a pin shoulder to improve part manufacturing and reduce costs. A pin shoulder will promote vertical pin stability inside the insulator.

Regarding Integrated Technologies:
Press-fit bushings and screw-locks are examples of fastening hardware integrated into custom assemblies. O-Rings, thermoset gaskets, and potting compounds are methods to achieve an environmental seal. The IP rating is a function of the required ingress prevention.

Manually placing fields of loose pins and socket receptacles onto a PCB is not only tedious but extremely cost-ineffective. Packaging discrete pins into molded insulators on tape and reel are the best path to increased productivity. Excessive heat can compromise press-fit retention. Poor coplanarity of a surface mount connector will produce poor solder joints and even leave the pin disconnected. These are some of the challenges when designing connector products.

Comments and suggestions are welcome.

Link of PDF presentation:
Pin and Socket Assemblies

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