Archive for August, 2009

Dry bake test results.

Saturday, August 29th, 2009

Printed circuit boards shall absorb moisture to the point of equilibrium. This shall occur as long as there is a source of moisture. Relative humidity provides an ample source of moisture for the absorption process. It is common for contract manufacturers to maintain a controlled environment that often relies on humidity to minimize static charge build up. Electro-static discharge (ESD) is damaging to assembled electronic components. Humidifiers are employed to maintain a 50% relative humidity environment. However, in minimizing one problem another is introduced. The humidity that is introduced to minimize ESD is absorbed into the printed circuit board and components alike.

In a production setting on a manufacturing shop floor, (more…)

Dry Bake Oxidation

Saturday, August 8th, 2009

As with any baking operation it is important to realize that the surface finish shall start to oxidize. There are many bake operations employed in printed circuit board manufacturing. When bare copper is baked at 300  deg F for an hour the copper turns color. The copper has become oxidized and must be cleaned prior to continued processing. The final solderable finish shall oxidize as well when exposed to heat. At the time of this posting the IPC and its members are currently working on a specification that deals directly with baking of printed circuit boards. The preliminary specification can be found posted on the IPC web site at… (more…)

Immersion Silver Storage and Handling

Sunday, August 2nd, 2009

Printed circuit boards that are coated with immersion silver must be handled with care and stored properly. The shelf life of immersion silver is typically 12 months. Properly stored boards protected from the environment can far exceed that limit. The following considerations must be taken into account in order to preserve the solderability of the finish. (more…)

Immersion Silver

Saturday, August 1st, 2009

Immersion silver is a solderable surface finish applied to the bare copper of a printed circuit board. The role of the immersion silver is to prevent the copper from oxidizing. When soldering to a board with immersion silver a copper-tin intermetalic alloy is formed. The silver is absorbed into the solder joint. Immersion silver is applied as a last operation. It is common for it to be applied to individual boards in piece or pallet form after the parts have been removed from the process panel. This minimized handling contamination and visual defects to the plated surface.

Immersion Silver has the following advantages… (more…)

When to apply ENIG.

Saturday, August 1st, 2009

ENIG (Electroless Nickel Immersion Gold) is applied to the bare copper of a printed circuit board during the fabrication process. When in the fabrication process should be a concern to the contract manufacturer or OEM responsible for assembling the components onto the bare board. If a fabrication drawing states that the printed circuit board shall have SMOBC (Solder Mask Over Bare Copper) then ENIG must be applied after the application of solder mask. There are some exceptions to the rule. (more…)