V-Score: Design Rules and Process Limits
A panel is separated into boards by breaking or cutting, and both methods leave a mark that the board carries for the rest of its life. The choice between scoring and routing is made from the board outline, the components that sit near it and the amount of stress the assembly can survive.
What Each Method Does
Scoring cuts a V shaped groove along both faces of the panel on a straight line, leaving a controlled web of material in the middle that snaps when it is bent. Routing removes the material between the boards with a cutter and leaves a tab, or a series of small bridges, holding each board in place.
The two methods leave different edges and apply different forces. A score line is separated by bending, while a routed tab is separated by cutting, twisting or snapping, and the stress the assembly sees depends on which of those is used rather than on the panel geometry alone. The edge that remains afterwards is a permanent feature of the finished product, and it is one of the few places where the fabrication method stays visible on the assembled board.
V-Score Geometry and Its Limits
The blades are ground at 30 or 45 degrees, and the standard rule is to cut one third of the board thickness from each side, leaving one third as the web. That web is what holds the panel together through assembly and what determines how much force is needed to break the board out.
The geometry restricts the method to straight lines, to panels at least about 0.6 mm thick, and to boards whose edges will not carry components. A curved outline cannot be scored, and a score on a thin board leaves a web that is too weak to survive the assembly line. The score is also a line of weakness in the panel, so the panel is handled with that in mind through printing, placement and reflow.
Tab Routing and Tab Design
Routing allows any outline, and the tabs are placed where they will not interfere with the assembly. A tab of 3 to 5 mm is typical, either solid or perforated with a row of small holes that let the tab be snapped by hand.
Those perforations are the mouse bites, usually a row of 0.5 mm holes on a 1 mm pitch, and the small bridges between them break cleanly when the board is flexed. The tab is a deliberate feature rather than a leftover, and its position is chosen in the panel design stage along with the tooling holes and the fiducials.
Component Keep-out at the Edge
Whichever method is used, components are kept away from the separation line. A chip capacitor placed within a millimetre of a score line sees the bending stress directly, and a crack that forms then appears as a failure much later in the product’s life. The keep-out is measured from the centre of the separation line rather than from the finished edge, because the break does not follow the line exactly on every panel.
The usual rule is a keep-out of about 1 mm from a score and 2 to 3 mm from a routed tab, with the larger figure used for ceramic parts and for anything on a flexing board. The keep-out is a board edge design rule rather than a note, and it is checked with the same design rule checker that verifies the outline.
Depanelization Force and Board Stress
Breaking a scored panel by hand applies a bending moment along the whole score line, and the boards either side of it flex in response. The strain can be measured with a strain gauge bonded near a sensitive component, and the same measurement is used to compare a hand method with a machine.
A depanelization machine that supports the board and applies the load along the line reduces the strain considerably, and a router reduces it further because it removes material rather than loading it. The measurement is the evidence, and it is taken on the first article with the components that are at risk populated. Where a router is used, the board is held by a fixture that supports it under the cut, and the tabs are cut in a sequence that keeps the board from dropping as the last connection is removed.
Edge Quality and What It Leaves
A scored edge has a characteristic angled profile and the laminate is exposed, so the edge is not coated and the glass fibres may be visible. A routed edge is smoother in outline but carries burrs from the cutter, and a burr on a copper edge can short against a chassis or a neighbouring board.
Both edges are inspected for delamination and for burrs, and the acceptance is written with a maximum burr height and a maximum delamination length. A burr is a handling hazard as well, since it cuts gloves and fingers and can shed metal particles into an assembly that is already populated. Our board quality notes describe how those figures are applied consistently between fabrication and assembly.
Choosing Between the Methods
Scoring is chosen where the outline is straight, the volume is high and the board can tolerate the edge profile. Routing is chosen for curved outlines, for boards with components close to the edge and for panels whose shape does not allow a blade to pass.
The board thickness moves the decision as well, because a very thick panel is difficult to score and a very thin one separates unpredictably. Where both methods are possible, the choice is usually made on the stress the assembly can take and on the cost of the tooling.
Verification and First Article
The first article checks the score depth or the tab dimensions, the edge quality after separation and the strain measured on a populated panel. The score depth is checked with a depth gauge or by sectioning one edge, and the figure is compared against the one third rule the drawing specifies.
A panel that separates with difficulty, or one that breaks elsewhere than at the score, has a depth that is wrong in one direction or the other. The check is made on the first panel of a lot rather than after a batch has been broken out by hand and the damage attributed to assembly. Where the score depth is outside its window, the panel is re-scored or the boards are separated in a machine that supports them instead of by hand.
Tooling, Cost and Documentation
Scoring needs a pair of blades ground to the panel, and routing needs a programme and a fixture, so the tooling costs are different in kind rather than in size. Scoring is cheaper for a long run of a simple outline, and routing becomes competitive as soon as the outline has any complexity.
The drawing should state the method, the depth or the tab size, the edge keep-out and the acceptance for burrs and delamination. Our board failure notes describe how an edge defect that is left unchecked turns into a cracked joint at a later stage, which is the cost of getting this item wrong.
FAQ
Can a board be scored on a curve? No, because the blade travels in a straight line, so a curved outline is routed. The rule is mechanical rather than a preference, and it is worth remembering when a shape is changed late in the design.
How deep should the score be? One third of the board thickness from each side is the usual figure, leaving a third as the web. That web is what survives the assembly line, so a deeper score is not automatically easier to break out.
Do mouse bites damage the board? They leave a slightly rough edge where the bridges break, and that edge is inside the keep-out for components. Where the edge is visible in the product, the tab position can be moved or the edge finished after separation.
