Press Fit Connector: Preparation, Placement and Process Control
A press fit connector makes its connection by deforming a compliant pin inside a plated hole. There is no solder, so the quality of the joint rests entirely on the geometry of the hole and the pin and on the plating inside it.
How a Compliant Pin Works
The pin is designed to deform elastically or plastically within the hole and to press against the barrel wall with a known force. The contact area that results is what carries the current and holds the pin against vibration.
The deformation has to be within the elastic range of the pin material or the connection relaxes. Our component tolerance notes describe the general principle.
Hole Tolerance Sets the Joint
The finished hole diameter has to sit inside a narrow window. Too large and the pin does not develop enough force; too small and the barrel is damaged during insertion.
The window is defined by the connector maker and it should reach the fabricator unaltered. Our hole copper notes describe the plating that goes with it.
Plating Inside the Barrel
The plating thickness and its ductility decide whether the barrel survives the insertion. A brittle deposit cracks when the pin expands it, and the crack may not be visible from the surface.
The plating thickness is measured on a coupon and the ductility by a separate test. Our plating notes describe both.
Insertion Force and Equipment
Insertion force is a proxy for the joint, and it is easy to measure on the line. A press that records force against distance gives a curve for every connector, and a curve that differs from the reference is a warning.
The equipment should be set up so that the force is applied along the pin rather than at an angle. Our placement notes describe the alignment that matters.
Backplanes and Large Connectors
A backplane carries many pins at once, so the total force is high and the board has to be supported while it is applied. A board that flexes during insertion loads some pins before others.
Support and pin sequencing are therefore part of the process. Our connector notes describe the assembly arrangement.
Rework and Repair
A press fit pin cannot be reinserted indefinitely, because the barrel and the pin both deform permanently. The number of insertions allowed should be stated by the connector maker and recorded on the line.
Where a pin is removed, the hole has to be assessed before a replacement goes in. Our rework notes describe the assessment.
Verification
The verification is a finished hole diameter measured on a coupon, a plating thickness and ductility result, and an insertion force curve recorded for the run rather than for one connector.
Our quality notes describe how the records are kept.
Process Control and Verification
On a design of this kind, compliant pin is the item that decides how the rest of the board is arranged. The process window is set by the narrowest step in the flow, so an improvement anywhere else shows up as margin rather than as yield until that step is addressed. A short note on the drawing about handling, storage or packaging is often worth more than an extra decimal place on a tolerance.
Where a value sits close to a process limit, the drawing should say so, since the shop can then open the process window rather than working to a nominal figure that carries no tolerance. A stack-up that is drawn rather than described removes most of the ambiguity from a quotation, and it lets the fabricator price the board against the dielectric and copper weights that will actually be used.
Where the requirement is not written down, the shop supplies its own default, and the default is chosen for the process rather than for the design. The measurements that matter are the repeatable ones: conductor width and spacing, annular ring, finished hole size, plating thickness and surface finish are all verifiable on a coupon that travels with the panel.
Running a first article through the same checks as the production panel confirms that the two agree, and that comparison is the cheapest form of process control available at prototype stage. Keeping a sample from the panel turns a dispute into a measurement, because the same coupon can be re-examined by both parties without rebuilding the batch.
Reviewing the design before the data is released is cheaper than correcting it after the panel is in the tank, because every step downstream inherits the decision made at the front end.
Process Control and Verification
On a design of this kind, compliant pin is the item that decides how the rest of the board is arranged. The process window is set by the narrowest step in the flow, so an improvement anywhere else shows up as margin rather than as yield until that step is addressed. A short note on the drawing about handling, storage or packaging is often worth more than an extra decimal place on a tolerance.
Where a value sits close to a process limit, the drawing should say so, since the shop can then open the process window rather than working to a nominal figure that carries no tolerance. A stack-up that is drawn rather than described removes most of the ambiguity from a quotation, and it lets the fabricator price the board against the dielectric and copper weights that will actually be used.
Where the requirement is not written down, the shop supplies its own default, and the default is chosen for the process rather than for the design.
Process Control and Verification
On a design of this kind, compliant pin is the item that decides how the rest of the board is arranged. The process window is set by the narrowest step in the flow, so an improvement anywhere else shows up as margin rather than as yield until that step is addressed. A short note on the drawing about handling, storage or packaging is often worth more than an extra decimal place on a tolerance.
Where a value sits close to a process limit, the drawing should say so, since the shop can then open the process window rather than working to a nominal figure that carries no tolerance.
Process Control and Verification
On a design of this kind, compliant pin is the item that decides how the rest of the board is arranged. The process window is set by the narrowest step in the flow, so an improvement anywhere else shows up as margin rather than as yield until that step is addressed. A short note on the drawing about handling, storage or packaging is often worth more than an extra decimal place on a tolerance.
A first article check confirms that the process and the drawing agree on the points listed above, and that the coupon data supports the values used in the design.
Where a measurement falls outside the expected window, the sample is retained so that the cause can be established before the balance of the batch is released.
FAQ
Can a press fit joint be soldered as well? It can, but soldering removes the ability to rework the connector and it adds a thermal cycle to the pin. The choice should be deliberate.
Does the hole need to be countersunk? Usually not. The pin is designed for a straight barrel, and a chamfer that is too large reduces the contact length.
What does gopcb provide for press fit assembly? We provide finished hole diameters measured on a coupon against the connector maker window, plating thickness and ductility results, insertion force curves recorded per connector, board support during insertion, and a stated limit on the number of insertions per hole.
