Issue link: https://iconnect007.uberflip.com/i/1547450
NOVEMBER 2026 I SMT007 MAGAZINE 59 entire joint. If that sharp edge bears against the root, it acts as a stress concentrator and a cutting tool at the same time. Specify a chamfer or countersink of about 0.5 mm at 45 degrees on the board's entry side, or confirm that the stud's root fillet—0.4 mm minimum, 0.6 mm for glass-filled resins—sits fully below the board rather than inside the hole. Second, plating. Stake holes should be non-plated (NPTH). A plated barrel adds a hard copper edge against soft plastic and puts a conductor exactly where molten material is about to flow, for no benefit whatsoever. Keep it bare laminate, and make sure the fab notes say so; some fabricators plate every- thing unless told otherwise. Position the hole center at least two stud diameters from the board edge, and treat that as a floor, not a target. The same edge-distance rule already applies to the plastic part; the board should not be the weaker half of the pair. Give the Formed Head Room to Land The formed head finishes at roughly twice the stud diameter and half the stud diameter tall. The keep-out zone has to be bigger than the head because during forming, softened plastic flows outward, and the forming tool that shapes the head is larger than the head it leaves behind. A practical rule: Keep everything off a ring of at least 1.5 times the stud diameter, measured as a radius from the hole center, on the top side of the board (Figure 3). For a 3 mm stud, that is a 4.5 mm radius, a 9 mm circle of nothing. Inside it: no traces, vias, test points, fiducials, component bodies, or solder joints. Molten plastic does not read your netlist. A trace that wanders under the head becomes a trace embedded in the joint, and the finished assembly still has to pass acceptance under IPC-A-610 2 ; a head that has flowed over a via or pinched a conductor is an easy reject. The bottom side needs its own keep-out, for a different reason. The board seats on the boss's shoulder or a standoff, and the full clamping load of the joint passes through that annular contact patch. A trace routed through it takes the entire preload across its own thickness, which is a reliable way to manufacture an intermittent. Keep the seating ring bare on the bottom side, sized to the boss outside diameter, which typically runs two to three times the stud diameter. IPC-2221 and its rigid-board companion IPC-2222 treat mounting and mechanical support as design inputs to be specified on the drawing, not artifacts to be discovered at assembly. 3,4 Stake locations deserve the same treatment as any other mounting hole: dimensioned, keep-outs drawn, and noted. Half the Job Get the hole right and keep the copper clear, and you have handled everything about heat staking that lives inside your CAD tool. That is half the job. The other half happens in about four seconds on an assembly line that you may never visit: A tool comes down, the board takes a load it was never analyzed for, and a little heat lands a few millimeters from your solder joints. The Board Gets Loaded Like a Structural Part, Because for a Few Seconds It Is One During staking, the press drives a tool against a stud standing on a boss that holds your board. The load path runs through the laminate. How much load depends on the equipment: displacement- controlled presses form to a programmed height Figure 3: Keep-out zone at a stake site, top view. The formed head finishes at 2 × D; the keep-out ring extends to at least 1.5 × D radius from the hole center, and copper routes around it, never through it.