High-precision small metal parts and screws with clean, corrosion-resistant finishes.
Electronics assemblies use small screws in thin sheet, plastic bosses and die-cast housings. Almost nothing here fails for lack of strength — it fails because of a particle, a burr, a blistered deposit or a screw that cams out and scars a visible surface. Cleanliness, plating adhesion and burr control are what incoming inspection actually rejects on, and the coating has to be thin and uniform rather than thick and durable.
| Property class | 4.8 / 8.8 · A2-70 stainless where specified |
|---|---|
| Hardness | case 450–560 HV on cold-headed / self-tapping screws |
| Materials | SWCH carbon steel · S20C · SUS304 |
| Coating system | Zn + Cr3+ clear / blue · zinc phosphate as a paint base |
| Coating thickness | 3–8 µm Zn (thin, for recess and thread fit) |
| Salt spray (NSS) | 48–120 h NSS |
| De-embrittlement bake | decided by hardness, not size — review case-hardened screws |
| Inspection methods | ISO 3497 (XRF) · adhesion check · RoHS / REACH declaration |
Electronics parts are specified tighter on thickness and cleanliness and looser on strength than any other sector here. A thickness range with a stated maximum is more useful to us than a long salt-spray requirement.
A metallic particle from a burr, a flake of plating or dried salts left by an incomplete rinse can short a board or jam a mechanism. The sector controls this with a stated cleanliness limit — an extraction with a gravimetric residue or a particle count per part — because "clean" is not a measurement. A part that looks clean under a bench lamp is not a result anyone can accept or reject.
Coating that lifts as a blister or peels at the drive recess almost always traces back to pre-treatment: cold-heading or thread-rolling oil not fully removed, smut left after pickling, or an interrupted rinse. On an electronics screw this is a contamination defect as much as a cosmetic one, because a blister on the head sheds flakes straight into the assembly.
A burr at the recess or on the thread lead stops the driver bit seating, causes cam-out, and scars painted or anodised faces on the way out. Burrs also plate badly — the deposit thins over a sharp edge, so that edge becomes the first place red rust appears even when the average thickness is comfortably in spec.
Electronics screws are plated thin precisely because an M2 or M3 thread and a small recess have very little room. Zinc grows the effective pitch diameter by roughly four times the local thickness, which is a large fraction of the tolerance on a small thread, and a filled recess changes how far the bit engages. Thin, uniform, well-rinsed deposits matter more here than salt-spray hours.
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We use trivalent (Cr3+) passivation, which is specified precisely because it avoids hexavalent chromium. Send the substance specification you have to satisfy and we will confirm in writing what the process uses. A colour on its own — clear, blue, black — does not prove which chemistry produced it.
Yes, provided the thickness is specified as a range with a maximum, not only a minimum. Zinc grows the effective pitch diameter by roughly four times the local thickness, which is a large share of the tolerance on a small thread. Send the thread class and the gauging requirement with the drawing and we confirm the fit before the lot runs.
It depends on hardness, not on size. ISO 4042 makes the decision by hardness and strength: parts at or above about 320 HV, and case-hardened parts, are the ones at risk. A plain class 4.8 screw normally is not; a case-hardened self-tapping screw should be reviewed. Send the hardness or the class and we confirm before plating.
The bands on this page are typical industry values, not a guarantee for any specific part. The governing drawing, customer specification and standard always take precedence, and every value is confirmed against your part before production. V.S. Heat Treatment operates under ISO 9001:2015; no other certification or sector approval is claimed.
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