A silicone heater is a resistor circuit between two sheets of rubber. The circuit itself is the reliable part — foil or wire, dimensioned once, and it will outlast everything around it. What fails is the bond: either something expands between the layers, or the layers move.
Both failures are usually blamed on the material. They are almost always process decisions made weeks earlier.
Bulging: what is actually inside
A bubble under the surface of a silicone heater is not air from outside. It is gas that was already in the compound, held in place until the operating temperature gave it enough pressure to separate the layers. Cure by-products and low-molecular-weight fractions are the usual source.
The fix is upstream of the laminating press. A platinum-cured, low-volatile compound that is fully post-cured before lamination has nothing left inside to expand at 150–200 °C. Skipping or shortening the post-cure saves a few hours and moves the failure into the customer's process, six months later, at temperature.
One field signature is worth knowing: bulges appear first where the heater is hottest, not where the outline is weakest. That is gas, not adhesion.
Delamination: the glue line is the weak link
When the layers separate with no bubble, the cause is the bond. An adhesive line — even a good pressure-sensitive or addition-cure adhesive — is a third material between the silicone and the silicone. It has its own modulus, its own creep behaviour, and its own thermal expansion. Under a few thousand hours of cycling at temperature, it creeps from the edge inward, and the heater opens up like a book.
Hot-vulcanized lamination removes the third material. The layers are cured into one monolithic part: no glue line to creep, and no interface to peel. There is also nothing to outgas from the adhesive itself, which matters on the semiconductor side of the business.
Three gates, in order
| Gate | What is controlled | What it prevents |
|---|---|---|
| Compound | Platinum cure, post-cure schedule, volatile content | Gas expanding into a bubble at temperature |
| Lamination | Hot vulcanization instead of adhesive bonding | Creep at the bond line, peeling from the edge |
| Inspection | 100 % hipot and resistance test per piece, lot traceable | A unit with a damaged element reaching the carton |
None of the three is exotic. What makes them work is that all three are applied on the same part, and the third one proves the first two did not quietly drift.
What to ask before you approve a sample
- Is the compound post-cured before lamination, and for how long? “Post-cured” without a schedule is a word, not a process.
- Is the lamination vulcanized or glued? If glued, ask which adhesive and what its continuous temperature rating is.
- Is every piece hipot tested, or is it sampled? Sampling tells you about the batch; the customer needs to know about the piece.
- What is the lot number on the label? Without traceability, an eight-month failure is unfalsifiable.
When it is not the heater's fault
Two failures get blamed on lamination and belong elsewhere. The first is a rough or warped metal face: the heater cannot conduct heat away fast enough at a local high spot, the silicone over-tempers there, and the bond gives up. The second is running above the clamping rule — on metal, above roughly 2.5 W/cm², life follows contact quality rather than the compound.
The boundary is the same one we state on the product page: silicone swells in fuel and aromatic oils. In that service FKM is the right material, and no amount of lamination quality fixes it.
Details of the build are on the silicone rubber heater page; the numbers that decide a specification are in Heater selection: five numbers.
Send a drawing and the operating condition, and we will quote the build.