Overview
ISO 7587:1986 - "Electroplated coatings of tin-lead alloys - Specification and test methods" specifies requirements and test methods for electrodeposited tin‑lead alloy coatings with tin content in the range 50–70 % (m/m). The standard covers composition control, thickness classification, appearance, adhesion, porosity and solderability requirements, and includes procedural guidance (e.g., sampling, heat treatment and use of undercoats). Annexes describe analytical and referee methods for composition and adhesion testing.
Key topics and technical requirements
- Alloy composition: Coatings covered have nominal tin content from 50 to 70 % (m/m). Annex A provides an iodometric analytical procedure for tin determination and recommends beta‑backscatter as a routine technique.
- Coating classification: A coded format defines basis metal, undercoat and minimum thickness, alloy composition and surface finish (matt, bright or flow‑melted). Purchaser should supply the full classification code and any samples.
- Thickness requirements: Minimum coating thicknesses are specified according to a four‑level service condition scale (mild to exceptionally severe) and vary with basis material (e.g., copper vs other metals). Thickness is measured per referenced methods (ISO 2064 and related standards).
- Appearance and acceptance: Significant surfaces must be free from visible defects (blisters, pits, cracks) and meet the purchaser’s finish sample or specification. Flow‑melted surfaces have specific acceptance notes.
- Adhesion and porosity testing: Adhesion tests are described (see annex C) and porosity testing is required if specified - using neutral salt spray (ISO 3768) for ferrous substrates or ISO 6988 methods for non‑ferrous materials.
- Solderability: If required by the purchaser, solderability tests are performed in accordance with IEC Publication 68‑2‑20 (Test Ta or Tc for PCBs), including options for accelerated ageing prior to test.
- Pre/post treatments and heat: Guidance on stress relief for cold‑worked steels prior to plating and limitations on post‑plating heat treatment (hydrogen embrittlement relief after plating is impractical).
- Scope exclusions: Threaded components, bearing overlays, unfabricated sheet/strip/wire coatings and plating of very high‑strength steels are excluded.
Applications and users
ISO 7587 is used by:
- Electroplating service providers and process engineers to define tin‑lead plating specifications.
- PCB manufacturers and electronics assemblers concerned with solderability and whisker resistance.
- Quality control and inspection teams for sampling, thickness, composition and adhesion testing.
- Procurement and design engineers specifying protective and solderable finishes for telecom, consumer electronics and general electrical components.
Related standards
Referenced standards include ISO 1463, ISO 2064, ISO 2177, ISO 2819, ISO 3497, ISO 3543, ISO 3768, ISO 4519, ISO 6988 and IEC Publication 68‑2‑20 - these cover thickness measurement, adhesion/test review methods, corrosion/porosity tests and solderability testing.