PCB surface finishes: select by interconnect application
Surface finishes must meet soldering, contact, storage, and actual assembly thermal-history requirements together. Distinguish solderable pads, edge-connector contacts, and wire-bond pads before selecting uniform or selective finishes; color and gold content cannot replace plating and application definitions.
| Surface Finish | Applicable interconnect use | Trade-offs that need confirmation |
|---|---|---|
| ENIG | Fine-pitch soldering and flatness | Nickel/gold layer requirements, process control, and high-frequency effects |
| OSP | Soldering, cost, and flatness | Storage/open-package time limits, thermal history, and rework |
| HASL | Soldering with acceptable flatness requirements | Fine pitch and pad coplanarity review |
| Immersion Tin / Immersion Silver | Specific assembly and connection requirements | Environment, storage, packaging, and assembly time |
| Electroplated Gold / Gold Fingers | Edge-connector contacts or another specified plated contact | Gold type, thickness, wear, and electroplating leads |
| Selective Surface Finish | Different interconnect applications on one board | Area boundaries, processing sequence, and cost |
How to agree on storage duration and multiple assembly cycles
Third-party typical storage periods cannot be presented as guarantees for every factory order. Determine solderability periods from actual finish processes, packaging, storage, and reflow/rework counts; record production, package-opening, and assembly dates. RF areas also require evaluation of nickel layers, roughness, and solder mask.
Acceptance Evidence
Plating requirements specify measurement locations, methods, and sampling; determine soldering-performance verification according to customer assemblies and thermal history. Contact areas require separate mating-cycle and contact-resistance tests with the actual connector; ENIG pads are not automatically hard-gold contacts.
Inputs and outputs
Inputs are component pitch, soldering/contact/bonding uses, storage duration, assembly-cycle count, RF constraints, and area drawings. Outputs are finish selection, regional process drawings, plating/solderability inspections, and packaging requirements. Confirm the available finish combinations for the current project with the responsible fabricator.
Gold-Finger PCBs, High frequency, RoHS evidence, Submit surface finish requirements
Engineering reference | PCB surface finishes: soldering, contact, and storage requirements: methodological reference; third-party design methods or material documentation do not represent KFPCBA manufacturing capabilities.
Select finishes separately for solderable pads, edge contacts, and wire-bond pads
| Application | Reviewable surface finish directions | Conditions that must be clear |
|---|---|---|
| Solderable Pads | ENIG, OSP, immersion tin, immersion silver, HASL | Pad pitch, flatness, thermal history, storage, and packaging |
| Edge-Connector Contacts | Gold fingers with specified nickel and gold thicknesses | Gold type, thickness, hardness, bevels, and contact life |
| Wire-Bond Pads | Qualify the finish for the wire material and pad requirements | Wire, layer structure, cleaning and storage, and sample verification |
| Different Interconnect Regions | Selective Surface Finishes | Area boundaries, electroplating leads, operations, and costs |
Standard ENIG solder pads are not automatically wear-resistant hard-gold contacts; the historical Bonding label also cannot replace wire-bond qualification for the specified wire and pad surface.
