Sometimes the simplest solutions are the best.
I can’t describe how many times I sat across from an engineer describing his exotic approach to an interconnect challenge, only to show him that there is a much simpler, easier and cost effective approach to achieving the same result. It’s not the fault of the engineer, he was unaware that a simple solution existed.
One such simple solution is with nailhead pins. Nailhead pins are of simple geometry, but they can serve many purposes. They are simple in construction, typically consisting of a large diameter, flat-faced head, followed by a series of pin diameters. Nailhead pins are easy to modify and manufacture, which makes them a very flexible and cost-effective interconnect.
Here are some common applications where these components can be used to simplify your design.
Nailhead pins make natural mating surfaces for spring pin contacts: gold-plated PCB lands are typical mating surfaces for SLCs, but what happens if the engineer is faced with an application that the spring pin cannot reach the PCB? Well, one solution is to elevate the gold plated connection off the surface of the PCB through the use of nailhead pins. Another important usage is in high-cycle applications, when you would not want to plate heavy gold on all the PCB pads, but you can insert a single nailhead pin plated with heavy gold for durability. This is a tremendous cost savings tip.
Another practical application that most engineers do not consider is that the nailhead pin can be easily designed to become a low cost, precision distance mechanical spacer.
These simple devices can be designed with a retention feature for packaging multiple pins into an array. This makes PCB assembly of multiple pins easy.
Additionally, if an SLC piston is 1 mm (0.40 in.) in diameter, specifying a nailhead pin with a shoulder diameter of 1.77 mm (0.70 in.) creates an easy target for the SLC to mate to.
They are also an easy choice for engineers designing pinned adapters. The large pin head can either be SMT soldered to the bottom side PCB pad or it can be placed through-hole for stronger mechanical attachment. Nailhead pins can be designed with press-fit retention features for solderless connection to the PTH. For a through-hole nailhead pin, make the finished plated hole at least 0.1 mm (0.004 in.) larger in diameter than the nailhead pin tail. For SMT designs, make the PCB SMT pad at least 0.127 mm (0.005 in.) annular ring larger than the nailhead shoulder to achieve a good solder fillet.
Nailhead pins can be designed with press-fit retention features for solderless connection to the PTH. For a through-hole nailhead pin, make the finished plated hole at least 0.1 mm (0.004 in.) larger in diameter than the nailhead pin tail. For SMT designs, make the PCB SMT pad at least 0.127 mm (0.005 in.) annular ring larger than the nailhead shoulder to achieve a good solder fillet.
In another application, they can be used as a contact pin for thin-flex PCBs. They provide a low-profile method of attaching pins without the added height of a pin body. For production assembly runs nailhead pins can be supplied in deep drawn tape for pick and placement. Nailhead pins can be easily modified to provide the precise amount of extension above and below the thin-flex PCB. In some cases, they don’t need to be pins but can be any flat-sided interconnect with a flat base termination. An example might be a flat-sided face soldercup for wire attachment but the flat side is used as the mating surface for a soldercup spring pin contact.
Nailhead pins can be used as PCB test points. Creating PCB I/O test points is easy with nailhead pins. The pin tail allows for quick alligator clip attachment from text equipment. Nailhead pin diameters can be made as thin, for high-density applications, or as large, for more robust usage. They can be plated gold or tin, depending on preference and typically guided by the environment the pin surface will be exposed to. They are used in both through-hole and SMT applications.
Probably one of the least known and used applications for a nailhead pin is as a mechanical standoff. Since this type of pin is simply a series of diameters, the diameters can be used as shoulders to set a precision spacing distance between two PCBs. This is especially useful for applications that require mating modules to come a hard stop and not damage components below.
Martin Houlroyd is Principal Engineer/Marketing Specialist at Preci-Dip. He has worked in the interconnect industry for 35 years. Email him at email@example.com.