Metal
Medical heart-rate strap with 316L stainless insert
- Route
- Degrease, blast, plasma, silane primer, in-mould cure
- Result
- Tens of thousands of flex cycles without edge lift; passed sweat ageing
Silicone Bonding: by Substrate
Silicone to metal, engineering plastics, glass and ceramics, and PCBA all follow one sequence: clean and activate the surface, choose the primer for that substrate, then bond in the mould during vulcanisation. This page lists pre-treatment, moulding route and typical parts per substrate, plus nine production cases.
Substrate matrix
Five substrate families, five different pre-treatments
One press can mould any of them. The primer and activation cannot be shared.
1. Silicone + metal
| Substrate | Pre-treatment | Process | Typical parts |
|---|---|---|---|
| 316L stainless / steel | Degrease, blast, silane primer, plasma | Compression moulding, in-mould cure | Watch-band inserts, medical sensor frames, cookware and lock overmoulds |
| Aluminium / anodised | Degrease, etch, primer; anodic layer compatible | Compression or LSR injection | Grip mouldings, connector boots, aluminium frame edge protection |
| Copper / brass / phosphor bronze | Remove oxide, anti-corrosion primer to stop sulphide attack | Compression moulding | Dome-switch contacts fully encapsulated, terminal insulation sleeves |
| Zinc / die-cast alloy | Abrade, degrease, metal primer | Overmoulding | Appliance keys, housing grips |
2. Silicone + engineering plastics
| Substrate | Pre-treatment | Process | Typical parts |
|---|---|---|---|
| PC | Plasma + primer; bonds directly in the mould | Compression or LSR | Glass-screen PC frame edge wrap (±0.03 mm), two-tone wearable housings |
| ABS | Degrease + primer; low-temperature cure only | Compression moulding | Earbud buttons, appliance switches, two-tone cosmetic parts |
| PA6 / PA66 (glass-filled) | Flame or corona + nylon primer | In-mould cure | Cookware handles, wearable frames, sealing structures |
| PBT / PPS | Degrease only | LSR injection | EV connectors, high-temperature seals |
| TPU | Plasma + soft-substrate primer | One-shot compression | Two-tone straps, hard-soft protective sleeves |
| PP / PE | Corona or flame + PP primer (mandatory) | Compression moulding | Child-care products, waterproof housings (harder route) |
| PET film | Plasma + thin primer | Compression lamination | Screen-protector edge wrap, flexible film composites |
3. Silicone + glass / ceramic
| Substrate | Pre-treatment | Process | Typical parts |
|---|---|---|---|
| Tempered glass | Alcohol degrease + plasma; no blasting | Self-adapting floating mould | Full edge wrap: anti-tamper, no sharp edge, drop cushioning |
| Alumina ceramic | Clean + silane coupling primer | Compression moulding | Medical ceramic electrode encapsulation, sensor protection |
4. Silicone + electronics
| Substrate | Pre-treatment | Process | Typical parts |
|---|---|---|---|
| PCBA (coin cell, Li-po, dome switches, slide switches) | Board clean + low-temperature cure, temperature controlled throughout | Low-temperature, low-pressure encapsulation | Medical temperature and heart-rate modules, wearable insulation boots, anti-tamper housings |
5. Silicone + other materials
| Combination | Process | Typical parts |
|---|---|---|
| Silicone + silicone (two-tone) | Simultaneous cure with mould segregation — no middle plate, no second shot | Two-tone watch bands, multi-colour keys, cosmetic parts |
| Silicone + glass fibre / fabric / webbing | Pre-impregnated fabric, compression lamination | Sports guards, webbing-bonded straps, waterproof textile composites |
| Silicone + epoxy / FR4 | Plasma + primer | Industrial board insulation, epoxy housing sealing |
Verified cases
Nine production cases, metal to PCBA
All bonded in the mould during cure, none glued afterwards. The process route and results can be read against your own project.
Plastic
Thermometer housing, PC two-tone overmould
- Route
- Plasma, PC primer, compression moulding
- Result
- Bond intact after -20 to 85 °C cycling; stable sealing
Glass
Phone screen protector, full silicone edge wrap
- Route
- Glass clean, plasma, floating mould
- Result
- Edge sealed, resists prying, fewer chipped corners on drop
Electronics
Medical temperature module, full encapsulation
- Route
- Board clean, staged low-temperature low-pressure cure
- Result
- No measurable battery cycle loss, million-press keys, IP67
Glass-filled PA
Outdoor device grip overmould
- Route
- Corona, nylon primer, in-mould cure
- Result
- UV and rain ageing without interface cracking
PBT connector
EV connector seal overmould
- Route
- LSR one-shot injection
- Result
- Stable bond at 125 °C continuous; insulation verified
Two-tone
Two-tone smartwatch band, one shot
- Route
- Simultaneous cure with mould segregation
- Result
- Clean colour boundary, tears in the rubber not at the interface
Ceramic
Medical ceramic electrode encapsulation
- Route
- Clean, silane coupling primer, compression
- Result
- No lift after long sweat contact; stable signal
PET film
Flexible film sensor lamination
- Route
- Plasma, thin primer, low-pressure compression
- Result
- Film undistorted, uniform bond, no delamination on flex
By material
One article per substrate
Failure modes, pre-treatment, primer, structural points and tests, written for the drawing review.
Articles for the other substrates are in preparation; the matrix and cases above cover the routes in the meantime.
Principles
Mechanism first, substrate second
Why interfaces fail, how long the activation window lasts, which primer family fits, and how electronics can be encapsulated at low temperature — the shared logic behind every substrate.
SurfacePlasma activation: a 30-minute windowHow surface energy decays and how to hold the window
Failure analysisEight failure modes in silicone overmouldingDelamination, edge lift, voids and interface corrosion
MaterialsCan you skip the primer? Limits of self-bonding LSRWhich substrates allow it, and where it should not be used
SelectionMaterial and primer matrixWhich primer family fits which substrate
SelectionProperties libraryHardness, tear, temperature and extractables by grade
Next step
Send the substrate, duty and structure
We recommend primer and process from the substrate grade, service environment and joint design. Physical samples can be compared interface to interface.
Related products
- Skin-contact silicone for temperature monitoringMedical-grade encapsulation and skin-contact structures
- Material and primer matrixWhich primer family fits which substrate
Sample request
Send the substrate grade, drawing or sample, service conditions (temperature, media, flex cycles) and target tests.
Request a sampleDatasheets & certificates
Material compliance declarations, FDA / LFGB test reports, RoHS reports and dimensional inspection records are available per project.
Tell us the application and target market — the document set differs by market.
Request documentsEnquiry
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