Designing die-cut lids and cards: what to put on the spec

Most first specs are close. What they miss is usually not the outline but the information around it: which dimensions matter, which face of the material goes where, how the part will be used. A cutter can't guess those, and a wrong guess shows up as a lid that won't sit in the sealer or a card that tears when the device goes in. This article walks through what to put on the spec for a lid and for a card, how to call out tolerances, and which files to send.

Every spec: the basics

Whatever the part, start with the items a supplier needs to quote it and to cut the same part again a year later:

• Part number and revision. Put both in the title block. A reorder is only safe if everyone is cutting to the same revision.
• Material callout. Name the material, grade and thickness, for example heat-seal coated Tyvek® 1073B, or HDPE at a stated thickness in mil or mm. "Tyvek" or "plastic card" on its own is not enough to quote.
• Units. State them once and use them throughout. If you work in inches, give metric in brackets or the other way round, but make clear which one governs.
• Critical-to-function dimensions. Mark the few dimensions that decide whether the part works: the outline that must match the tray flange, the slot that holds the device. Those are the ones to hold tightly and inspect.
• Quantity. The quantity you need now and the volume you expect later. It decides how the part is best cut.

Lids

A die-cut lid has one job: cover the seal area on the tray flange completely, with a clear place for a gloved hand to start the peel. The spec should show how it does that.

Outline and corner radii

Draw the lid outline against the tray flange, or send the tray spec with it. Match the lid's corner radii to the flange corners, or make them slightly larger. Sharp lid corners can lift or catch in handling, and a corner that sits inside the seal area is a place a peel can start by accident.

Flange width and overhang

Show the flange width and where the seal sits on it. The lid should cover the full seal area and usually extends a little past the outer edge of the flange, so small placement variation on the sealer doesn't leave part of the seal uncovered. Show the overhang you want on the spec. If you don't know what your sealer needs, send the tray spec and tell us how lids are placed on your sealer, and we will suggest one.

Tab position and size

A tab is an unsealed area outside the seal that gives the user something to grip. Put it at a corner or along a side, wherever the user reaches first, and show which on the spec. Make it large enough to grip with gloved fingers, and keep it clear of the seal so it lifts freely. If the tray has a matching peel corner or a notch in the flange, show how the tab lines up with it.

Coated side, print area and keep-out

Coated Tyvek® has one coated face, and that face goes against the tray. Say so on the spec, for example "coated side down, toward tray", so there is no doubt on a printed or asymmetric lid.

If the lid is printed, show the print area as a box with dimensions from the lid edge, and the print content. Keep print out of the seal area and away from the tab where the user grips. Ink under the seal can change how the coating bonds, so treat print in the seal area as something to test, not assume. Lot numbers and expiry dates are usually added later, by a label or an in-line printer, so leave space for them if they go on the lid.

Peel direction

Add an arrow for the direction the lid peels back from the tab. It confirms which corner the tab belongs on, and on a printed lid it sets which way the print should read when the package is opened.

Cards

A mounting card holds the device in place inside a pouch or tray and keeps it off the barrier webs. The spec should show the card, the device on it, and how the device goes on and comes off.

Thickness

State the card thickness and, if it matters to fit or stiffness, its tolerance. Tolerances are quoted per part. Thicker cards are stiffer and hold heavy devices better, but tabs and slots in thick material are stiffer too, so a device that clips in easily on a thin prototype may need more force on a thick one.

Slots, tabs and holes

Dimension each feature and its position from a clear datum, usually one corner or edge of the card. Mark the features that grip the device, as opposed to those that only locate it, because those are the critical dimensions.

Keep the web of material between two cuts, and between a cut and the card edge, as wide as the design allows. Narrow webs and very small holes are the first features to tear or distort, when the device is loaded or when the card flexes in shipping. Give internal corners of slots and cutouts a radius rather than a sharp corner, since sharp internal corners concentrate stress and start tears. If a feature has to be small or close to an edge, flag it, and we will tell you whether it will cut cleanly in your thickness before we cut it.

Fold and score lines

If the card has to fold, for example to wrap a device or stand up in a tray, show each fold line, which way it folds, and the fold angle. We can cut score lines for folding in the same pass as the outline.

How the device loads and unloads

Add a view with the device in place, and note the direction it goes on and comes off. Think about the person at each end: an assembler loading cards on a line, and a clinician in gloves lifting the device out in the sterile field. A slot with a lead-in is easier to load; a tab that holds firmly in shipping still has to release without a struggle. Check that no edge or tab rubs a coated or delicate surface on the device.

Finally, check the card against the package. It has to fit the pouch or tray cavity without stressing the seals, and in a chevron pouch it should clear the chevron so the peel runs freely.

Tolerances

Put a tolerance on every critical-to-function dimension, and a general tolerance in the title block for the rest. Choose tolerances by what the part needs to do, not by habit. A tighter tolerance than the function needs costs more: it can mean a more precise die, slower cutting and more inspection, and it can reject parts that would have worked.

Flexible materials measure differently from rigid ones. A film part or a Tyvek® lid can change size slightly depending on how it is laid down, so say how a dimension is measured if it matters, for example flat and unrestrained. Our tolerances are quoted per part. Ask us what we can hold in your material before you finalize the numbers.

Files to send

• A PDF spec with dimensions. This is the document the part is cut and inspected to.
• A DXF or DWG of the outline. A clean 2D outline at full scale speeds up die design. Make sure it matches the PDF and carries the same revision.
• A 3D model of the device or tray, if you have one. STEP, IGES or STL helps us check fit, tab position and clearance.

If you only have a sketch, a photo or a sample part, send that. It is enough to start the conversation. We can draw the die-line from a sketch or sample for you to approve, free for parts we quote.

What we check before we cut

Before we cut a new part, we read the spec the way the die and your line will. We look at whether the part will cut cleanly in the material you've picked, where a tab, slot or corner is likely to tear or catch, and whether a lid covers the flange with room for a peel tab. If something in your spec will cause trouble on the die or on your line, we will tell you before we cut, along with what to change on the spec for the next round.

Next steps

For how specs fit into the path from first prototype to production, read prototype to production. For choosing the lid material itself, see coated vs. uncoated Tyvek® lidding. When your spec is ready, or nearly ready, send it through the engineering quote form.