I want the cheapest finish that works
OSPLF HASL
Both are a few cents a square inch. The catch is time: neither keeps for long before assembly, so they suit a board that is built soon after it is made.
PCB BASICS · 8 MIN READ
Which surface finish should you ask for?
The finish is the thin layer that keeps the copper solderable until the board is assembled. It is a few cents a square inch and it decides whether fine-pitch parts sit flat, whether the board still solders after six months in a box, and whether a high-frequency trace loses more than it should. Here are the 8 finishes in our catalogue, with what each one costs and what goes wrong with it.
Start from your problem
I have fine-pitch parts, 0.4 mm or tighter
OSPENIGEPIGENEPIG
A hot-air levelled finish leaves an uneven surface, and fine pitch needs a flat pad. These are the flat finishes in the catalogue that publish a pitch they hold.
The boards will sit in stock for months
LF HASLImm SnImm AgENIGEPIGENEPIGHard Gold
These publish a shelf life of a year or more. A finish that oxidises in three months turns into a soldering problem you will blame on the assembler.
It is an RF or high-speed board
OSPImm SnImm AgEPIG
Nickel under the gold is lossy at high frequency, so the finishes that publish anything better than poor RF performance are the ones to ask about.
I need gold wire bonding
ENEPIG
Only these publish gold wire bonding as supported. Getting this wrong is found at assembly, not at incoming inspection.
What each one costs
Dollars per square inch of board, as published in the research. OSP is the cheapest and ENEPIG the dearest of the priced finishes, a difference of about 3.1 times. On a 100 by 80 mm board that gap is small money; the reason to choose carefully is everything in the table below it.
- OSP0.05–0.07
- LF HASL0.05–0.08
- Imm Sn0.08–0.12
- Imm Ag0.08–0.12
- ENIG0.10–0.20
- EPIG0.12–0.22
- ENEPIG0.12–0.25
- Hard GoldVariable
All eight, side by side
| Finish | Cost $/sq in | Shelf life | Reflow passes | Min pitch mm | RF | Standard | Known risk |
|---|---|---|---|---|---|---|---|
| OSP | 0.05–0.07 | 3–6 mo | 4–6 | 0.4 | Excellent | IPC-4555 (draft) | Handling |
| LF HASL | 0.05–0.08 | 6–12 mo | 6+ | 0.5 | Poor | not published | Flatness |
| Imm Sn | 0.08–0.12 | 6–12 mo | 3–4 | 0.5 | Good | IPC-4554 | Whiskers/IMC |
| Imm Ag | 0.08–0.12 | 6–12 mo | 3–4 | 0.5 | Excellent | IPC-4553A | Tarnish |
| ENIG | 0.10–0.20 | 12+ mo | 5+ | 0.4 | Poor (Ni loss) | IPC-4552B | Black pad |
| EPIG | 0.12–0.22 | 12+ mo | 5+ | 0.3 | Excellent | Under dev. | Wire bond (EPIG) |
| ENEPIG | 0.12–0.25 | 12+ mo | 5+ | 0.4 | Poor (Ni loss) | IPC-4556 | Cost/complexity |
| Hard Gold | Variable | 12+ mo | not published | not published | not published | MIL-G-45204 | Cost/selective |
What to write on the request
Name the finish and the standard it is made to. "ENIG to IPC-4552B" leaves nothing to interpret; "gold finish" invites the cheapest gold-coloured thing in the building.
If the boards will wait before assembly, say how long. A finish chosen for a board built next week is the wrong finish for one that sits in a cupboard until the next production run.
Figures are read from our researched material catalogue and keep the units and ranges each source published. Confirm the exact grade and standard with your fabricator before an order: a finish is specified on the drawing, not agreed in an email.