Polyimide Tape for SMT Masking and Coil Insulation

Application notesPublished 07 November 2026Updated 07 November 2026

Polyimide tape appears on two kinds of line that ask opposite questions of it: an SMT or through-hole line that masks a site through reflow and then removes the tape, and a coil or transformer line that puts the same film in place as insulation and leaves it there. We convert both, and the specification that fits the first would be the wrong answer for the second.

Two lines, one material

On the assembly side, a typical request comes from an EMS plant in the Pearl River Delta running mixed-technology boards: a connector housing or a gold-finger array has to stay clear of paste, flux and solder wave, the board then goes through a lead-free reflow profile and, on some products, a selective soldering step and a cleaning cycle afterwards. The mask is removed by hand at a station after the oven, sometimes after the part has cooled in a magazine rather than straight out of the machine.

On the wound-component side, a request comes from a transformer or choke builder, in Malaysia or Indonesia, wrapping bobbin flanges, layer insulation and lead exits where the film has to survive the impregnation varnish or the potting step and then keep insulating for the service life of the unit. Nothing is peeled off afterwards. The same amber roll serves both, and the buyer specifying it for the second job is buying a different property set.

What loads the material in each case

The masking case is a thermal and interface problem. Peak temperature gets discussed, but the dwell in the upper band is what loads the adhesive, and the number of passes multiplies it: top-side reflow, bottom-side reflow, selective solder, then a bake for the cleaning or conformal step. The board temperature trace from a thermocouple tells more than the oven recipe does, because a heavy plane and a thin flexi do not experience the same profile in the same oven.

Removal adds two more constraints. Residue on a connector seat or a finger array is a cleaning operation somebody has to validate, and a siloxane film from a silicone coat is a wetting defect that surfaces at a later bonding, coating or wire-bond step rather than at the peel station. Release force is the third: too light and the strip lifts with the liner under an automated head, too heavy and an operator stretches it while peeling it.

The insulation case is a retention and edge problem. Adhesion has to survive the varnish or potting chemistry and the temperature cycling of the finished unit, and the film must not shrink or spring back at a cut corner where the creepage path is defined. Cut-edge condition matters more than it does on masking, so the cutting route and the dielectric requirement are discussed together rather than in separate emails.

The five things we review before quoting

One: which job the tape has, removable masking or permanent insulation, because that decides whether we shortlist on release level or on adhesion and withstand behaviour. Two: the measured thermal history, including every pass and the dwell, checked against the TDS for the ordered grade rather than against a family range. Three: both surfaces, since solder resist, bare copper, gold plating, bobbin plastic and varnish-coated windings are five different interfaces. Four: geometry and format, meaning strip width, cut length, whether the part needs windows or a slit liner for a feeder, and who applies it. Five: records, because a battery, medical or automotive customer will want the batch tied to incoming material, slitting date and inspection.

How we convert it

Roll stock is slit from jumbo rolls to the working width your station or applicator runs; widths below 10 mm are feasible on most materials once thickness, coat and edge requirements are reviewed at quotation. Masking and insulation shapes are cut by flat-bed for thicker laminates and lower volumes, by rotary for roll-to-roll series supply, and by laser where the outline is complex or the part is still moving. Where a part needs more than one layer, PI is laminated with film, foam, another adhesive or a liner to build the stack the assembly expects; the lamination route covers that. The die-cutting page lists the routes, and the achievable tolerance is stated against your drawing before tooling is cut.

What to send us

For masking: the thermocouple trace of your profile with pass count, the board photo or drawing of the masked area, the surface the tape sits on, how long the tape stays on before removal and who removes it. For insulation: the drawing of the part, the withstand or creepage requirement, the impregnation or potting chemistry, and the winding or assembly method the part is placed by. Either way, add the current grade name and a sample of what you run now, since the fastest route to a working polyimide tape specification is usually a comparison with what already almost works.

Rolls and cut parts ship from Shenzhen by express, air or sea, with LCL consolidation where that suits your inbound plan, and the commercial terms and timing are confirmed at quotation. Write to yantian0606@gmail.com or message us on WhatsApp at 8613554863137 with the profile and the part, and we will come back with a construction, a route and the test we would run to disprove it.

Commercial and process terms on this page are the questions a converter has to answer, not a standing offer. Order quantities, lead times, tooling charges, sample terms, freight and payment structures are confirmed at quotation against your drawing, your material and your destination, and only figures already published elsewhere on this site are stated as commitments.