The IPC-4556 PDF document is a valuable resource for:
It is widely known as the "universal finish" because it supports soldering, aluminum wire bonding, gold wire bonding, and contact applications on a single board. Key Technical Specifications (2015 Amendment)
The raises the bar for ENEPIG finishes. Key updates in this version focus on improving reliability in next-generation electronics: ipc4556 pdf
IPC-4556: Specification for ENEPIG Plating on PCBs (officially IPC-4556: Specification for Electroless Nickel/Electroless Palladium/Immersion Gold (ENEPIG) Plating for Printed Circuit Boards ) is the definitive industry standard for applying ENEPIG surface finishes. Developed by the IPC Plating Subcommittee (4-14) and amended in 2015, this standard provides strict requirements for ENEPIG layer thicknesses, quality assurance, solderability, and wire bonding performance.
Jake snorted. "IPC4556? That's just a bunch of bureaucratic nonsense. Can't we just use something that works?" The IPC-4556 PDF document is a valuable resource
Per the standard, layer dimensions must be statistically verified on a nominal pad area of 1.5 mm × 1.5 mm (or equivalent) using specific process standard deviation limits ( Plating Layer Minimum Thickness Limit Maximum Thickness Limit Key Engineering Function Diffusion barrier; prevents copper dissolution Electroless Palladium (Pd) Mitigates nickel oxidation; stabilizes wire bonds Immersion Gold (Au) Preserves shelf life; prevents air contamination Evolution of the Standard: From Base to Revision A
| Standard | Surface Finish | Typical Thickness | Primary Use Case | |----------|----------------|-------------------|------------------| | | ENIG (Electroless Nickel Immersion Gold) | 0.05-0.2 µm Au | Fine-pitch components, contact pads | | IPC-4553 | Immersion Silver (ImAg) | 0.1-0.4 µm Ag | High-frequency circuits | | IPC-4554 | Immersion Tin (ImSn) | 0.8-1.2 µm Sn | Press-fit connectors | | IPC-4555 | OSP (Organic Solderability Preservative) | 0.2-0.5 µm organic | Low-cost, short-shelf-life boards | | IPC-4556 | Thick-Film Copper | 10-40 µm Cu | High-power, heavy copper, thermal management | Developed by the IPC Plating Subcommittee (4-14) and
More information on how IPC-4556 compares to IPC-4552 (ENIG).
The device went on to become a huge success, and Emma's team was hailed as pioneers in their field. And Emma herself? She became known as the go-to expert on all things IPC4556 – a testament to the power of perseverance and attention to detail.