From my last post about the top-class work (ahem!) done by our Front End Team, I’d like to move onto one of the last processes carried out in printed circuit board manufacturing, i.e. the PCB finish.
The “finish” refers to the final coating which will cover the component pads. Sometimes, the via holes (the links through the board) are also finished but often these are left as copper and covered in Solder Resist.
The finishing stage of any printed circuit board manufacturing is really down to our customers’ preferences, although we can advise on this in the event of any uncertainty.
Lead Free Hot Air Solder Levelling. Bit of a mouthful? Try HASL for short! Containing about 99% Tin and a smidgeon of Copper, this has a shiny, silver appearance and is easily solderable. Compared to the, now unused Leaded Solder, this flows freely at about 510-520 degrees as opposed to 480-500 for Leaded. (Fig.1.)
Immersion Silver. Silver is a very highly conductive metal and supplies a very flat finish to the pads which is ideal for Surface Mount Components. It is easily solderable and ends up about 1 Micron thick on the pads. Its shelf life is shorter than HASL, and we recommend that printed circuit boards are assembled as soon as possible after delivery. (Fig.2.)
OSP or Organic Surface Protection. (Some say organic solderability protection but this REALLY is too much!) This is a very thin (about 0.5 Micron) organic chemical film finish and provides a very flat surface. Like the silver, PCB’s supplied should be assembled as soon as possible after delivery due to its shorter shelf life. (Fig.3.)
Electroless Nickel Immersion Gold. Shall we shorten it? I think so. ENIG, as it’s known is a thin layer of gold and nickel, plated onto the copper surface. Again, this method is gaining popularity due to its very flat finish and conductivity. (Fig.4.)
Hard Gold. This is a thick, electrically plated finish which is, as its name implies, very hard and durable. As far as our printed circuit board manufacturing process is concerned, it’s the most expensive of the finishes available and is most commonly used to plate edge connectors, such as those found in computer memory (RAM) cards and PC sound and video cards. (Fig.5.)
So there you have it. The choice is left to the customer and whatever finish best suits his PCB manufacturing requirements and as ever, you can rely on us to discuss this subject with you, should you require any further clarification.