WHAT IS IMMERSION SILVER FINISH?
Immersion Silver is the standard finish on PCB Train and is RoHS compliant. It is an improvement on HASL being exceptionally flat, and can replace Immersion Gold over Electroless Nickel (Au/Ni) for most applications. The use of Immersion Silver has no effect on customer's assembly processes. Immersion Silver Metallic Solderability Preservative is a 0.1 to 0.2 micron layer of metallic silver coated with an organic layer of solderability preservative.
ABOUT IMMERSION SILVER
- Immersion Silver Metallic Solderability Preservative is a 0.1 to 0.2 micron layer of metallic silver coated with an organic layer of solderability preservative.
- It is a "drop in" HASL replacement, requiring no change to assembly processes.
- It has excellent wettability for soldering.
- It is environmentally friendly.
- The solder joint strength is superior to that of AU/Ni pcb finishes.
- The resistance to environmental ageing is superior to that of organic solderability preservative (OSP).
- Flatness, electrical properties and solder joint strength are superior to HASL.
- For touchpad contacts, it is better than carbon ink and as good as Au/Ni finish, see the Motorola report into the use of immersion silver for keypad / touchpad contacts.
- It has similar performance Au/Ni for ultrasonic aluminium wire bonding.
- It can withstand multiple reflow.
- The process is supplied and supported by Macdermid PLC
ASSEMBLY GUIDELINES FOR IMMERSION SILVER
HANDLING AND STORAGE OF IMMERSION SILVER FINISHED PCBS
- Avoid finger contact with the Immersion Silver finish. It is recommended that gloves be used for handling panels/boards. Salts/acids from fingerprints may tarnish the finish, and impair solderability.
- The generally accepted shelf storage life for Immersion Silver is 6 to 12 months in dry conditions, the same as that for HASL.
- The bright appearance of Immersion Silver finished pcbs should not suffer from any yellow or black discolouration which will indicate contamination. If contamination is suspected, please contact us for advice.
- If pcbs have been in storage for some time, it is wise to perform a solderability test prior to assembly. For SMD applications this might consist of solder paste and reflow of a bare pcb. 100% solder wetting would indicate a satisfactory pass.
- When board cleaning or washing, surfactants and/or acid cleaners should not be used for bare boards with Immersion Silver finish. Only water washes should be used, with a pH > 6.0.
- Immersion Silver finished boards should be packaged to prevent exposure to air circulation. Storage could be in sealed bags or similar containers to exclude direct contact with air. Storage conditions should be < 30?C and < 50 % RH. Use sulphur free paper to interleaf parts.
- If Immersion Silver finished boards must be stress relieved for warp & twist problems, the boards should be tightly wrapped in aluminum foil to prevent oxidation of the silver which will affect solderability. The bake conditions are: Temperature 150deg C for 2 hours. If it becomes necessary to perform a bake to remove moisture, the time and temperature should be reduced to a minimum. Do not exceed 2 hours at 122deg C.