Archive for July, 2009

ENIG (Electroless Nickel Immersion Gold)

Friday, July 31st, 2009

There are many benefits to Electroless Nickel Immersion Gold (ENIG). The first benefit is a very flat and level surface to solder to. This makes ENIG ideal for fine pitch surface mount devices. Another benefit is that the nickel strengthens the structure of the plated through hole. There are some drawbacks to ENIG. ENIG is an unforgiving process. Once the coating is applied there is no going back. Techniques that could be used to remove the finish are also damaging to the copper. Tight chemical and process controls need to be in place at printed circuit board manufacturers in order to provide a quality coating of ENIG per IPC-4552. Defects with the ENIG plating process may not be discovered until (more…)

Dry baking printed circuit boards.

Sunday, July 19th, 2009

What most people don’t realise is that printed circuit boards are hygroscopic. They absorb moisture from the atmosphere like a sponge does water. Although the absorption process is much slower it does happen. The amount of moisture absorbed is measured and provided on material data sheets provided by most laminate manufacturers. For example  the moisture absorption limit listed on the Isola FR406 data sheet is 0.20 % measured on a .028 inch thick piece of stock laminate. Lead free assembly compliant laminates are even more hygroscopic. For example, Isola IS410 is 0.45 % measured on the same thickness material per the data sheet. Different grades of material from different manufacturers have different moisture absorption ratings. The percentage of moisture absorption increases when you add inner layer circuity and through holes. A low humidity environment results in a slow absorption rate. A high humidity environment results in a fast absorption rate. Moisture shall be absorbed to the point of equilibrium. Once equilibrium is achieved the absorption stops.

Printed circuit boards that have moisture in them can become (more…)