PCB Final Finish
Question:
Which of the following is the least expensive final finish for high volumeproduction?
A. Organic Solderability Preservative (OSP)
B. Hot Air Solder Leveling – tin lead/lead free (HASL)
C. Electroless Nickel Immersion Gold (ENIG)
D. Immersion Silver (ImAg)
E. Immersion Tin (ImSn)
B. Hot Air Solder Leveling – tin lead/lead free (HASL)
C. Electroless Nickel Immersion Gold (ENIG)
D. Immersion Silver (ImAg)
E. Immersion Tin (ImSn)
Answer:
The answer is A. Organic Solderability Preservative (OSP).
In high volumes, this is your lowest cost final finish. If you’re running low volumes, however, the money you save on a low cost finish can get quickly eaten up in poor assembly yields. If the OSP-treated PCBs aren't stored properly, or if they sit on the shelf too long, or if there are more than a few days between the first and final soldering cycles, you can expect solderability problems.
Figure 1 Organic Solderability Preservative (OSP)
For low volumes, HASL or ENIG are your best bet. HASL is not much more expensive than OSP, but it can cause assembly yield problems if your PCB design has fine pitch (20mil/0.5mm or less) devices. ENIG has great shelf life and is super “assembly-friendly.” In small volumes, the cost impact is insignificant as compared to the problems it can avoid.
Figure 2 Hot Air Solder Leveling (HASL)
Figure 3 Electroless Nickel Immersion Gold (ENIG)
What about immersion silver and tin? Like OSP, they’re good for high volumes, but shelf life issues make them a poor choice for low volumes.
Figure 4 Immersion Silver (ImAg)
Figure 5 Immersion Tin (ImSn)
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