Gold Finger Chamfer and Bevel Requirements for Edge Connectors

An edge connector meets its mating socket at an angle, and the chamfer on the leading edge is what allows it to enter without lifting the contacts or scraping them. The feature is small, it is produced after plating, and it is frequently left undefined on the drawing, which is why insertion problems on edge connectors are often traced to a bevel that nobody specified. This article covers the geometry, the process and the acceptance.

What the Chamfer Does

The chamfer guides the board into the connector and lifts the contacts gradually rather than in one step. Without it the leading corner of the board catches the contact and either bends it or scrapes through the gold, and both failures appear at the first insertion.

The feature also protects the plating. A gradual entry keeps the contact on the plated surface, while a sharp edge digs into the contact and transfers material, which changes the contact resistance after a small number of mating cycles.

Chamfer Angle and Depth

Typical geometry is an angle of 20 to 30 degrees from the board face, cut to a depth of 0.5 to 1.0 mm, with the cut extending across the full width of the finger pattern. The angle is a compromise between guidance and the loss of contact area that the bevel removes.

A shallow angle guides well but removes more length from the gold finger, and a steep angle removes less but gives less guidance. The value is chosen with the connector it will mate with, since the contact geometry of the socket decides how much lead-in is needed.

The depth is measured from the board edge to the start of the bevel, and it is checked on a sample rather than on every board, because the cut is made with a controlled tool.

How the Bevel Is Produced

The bevel is cut with a rotating cutter after the outline has been routed and after the gold has been plated, so the cut removes plating from the bevel face. The cut is therefore a mechanical operation that follows plating, and the sequence is stated on the drawing rather than assumed.

Some designs require the bevel to be cut before plating so that the bevel face is also plated, which changes both the process and the appearance. Where the bevel is intended to conduct, the plated bevel is the correct construction; where it is only a lead-in, the plated version is unnecessary cost.

Interaction with the Plating

Hard gold on an edge connector is usually 0.8 to 1.5 micrometres over 3 to 6 micrometres of nickel, and the bevel exposes the laminate and the copper beneath it. The boundary between the plated finger and the cut face is where the contact first touches, so its condition matters.

A cut that tears the plating or leaves it standing proud of the laminate produces a burr that scrapes the mating contact. The check is visual under magnification, and it is recorded with the sample that defines the acceptance limit. Plating thicknesses are described in our plating thickness guide.

Insertion Force and Wear

Insertion force is a function of the number of contacts, the contact geometry and the thickness of the board, and a rough bevel raises it noticeably. Measuring the force on a sample assembly against a specification gives a number that describes the whole interface rather than the board alone.

Wear follows the same geometry. A bevel that concentrates the contact pressure on a small area wears through the gold faster than one that spreads the load, and the worn area appears as nickel showing through after a few hundred cycles. The wear test is defined by the mating cycle count the product requires.

Variants: Stepped, Rounded and Double Bevels

Some connector families specify a stepped bevel, where the leading edge is thinned in two angles so that the board enters straight and then lifts the contacts. Others specify a rounded edge, which is produced by a router rather than a cutter and gives a smoother entry at the cost of less guidance.

A double bevel is used where the board has to be inserted from either face, and it requires both faces to be cut to the same depth. Whichever variant applies, the drawing has to say so, because the shop will otherwise produce the single bevel it produces by default.

The variant is defined by the connector specification rather than by the board, so the connector part number belongs on the drawing beside the bevel note.

Inspection and Acceptance

Acceptance covers the angle, the depth, the consistency across the finger pattern and the condition of the cut face. A sample is taken from the first panel of a production run and measured on a comparator or by section, with the result recorded against the specification.

During production the check is visual; the second measurement point is after any tool change or sharpening, because a cutter that has been reground changes the geometry it produces. The connector itself is inspected against the criteria in our gold finger notes.

Drawing Notes That Define the Feature

The drawing should state the bevel angle, the depth, the face or faces to be cut, whether the bevel is plated and the acceptance on the cut edge. A note that says chamfer the edge without those numbers leaves the result to the shop’s default.

The bevel dimensions also need a datum, and the datum is the board outline after routing rather than the artwork, because the outline is what the cut is measured from. Defining the feature against the wrong datum produces a bevel that is correct on paper and variable on the panel. The outline and its tolerance are covered in our fabrication notes.

The cutter is a formed tool, and its geometry defines the angle it produces, so a worn cutter changes the bevel without any change to the machine setting. Cutter wear is tracked by count, and the tool is replaced or resharpened on that count rather than on the appearance of the edge.

Cutting produces dust from the laminate and from the plating, and that dust settles on the fingers beside the bevel. Where the connector carries low level signals, the residue is cleaned before packing, using a method that does not attack the laminate or the gold.

Boards are stacked or palletised after the bevel is cut, and a stack pressed against the cut face can chip the laminate at the edge. Packing therefore supports the board on its faces rather than on the bevel itself.

Where a panel carries several connectors that are broken out after the bevel is cut, the bevel is produced on the panel rather than on the separated board. That keeps the geometry consistent and avoids handling a small board against a rotating cutter.

Insertion testing on a sample uses the mating connector the product will actually meet rather than a generic socket, because contact geometry differs between connector families. A test with the wrong socket gives a force reading that describes neither product.

FAQ

Is the bevel cut before or after plating? After plating by default, which leaves the cut face unplated; where the bevel must conduct, the sequence is changed so that the bevel is plated as well.

What angle should be specified? Twenty to thirty degrees from the board face suits most edge connectors, and the exact value follows from the contact geometry of the mating socket.

Can a chamfer be omitted? Only where the connector has a long lead-in of its own, and even then the sharp corner tends to scrape the contact on the first insertion.