One of the misconceptions about Electroless Nickel Immersion Gold (ENIG) is that it remains solderable for an unlimited amount of time. This misunderstanding is based in the fact that gold is a noble metal. Noble metals are metals that are resistant to oxidation and corrosion. Hence the belief that ENIG remains solderable since gold is the metal that we see. Some people in the electronics industry are surprised when they learn that ENIG has a solderable shelf life of (more…)
Posts Tagged ‘solderability’
How does one identify the shelf life of a printed circuit board?
By convention the printed circuit board fabricator shall mark the printed circuit board with a four digit date code. The date code consists of a two digit week number ranging from 01 (the 1st week in January) to 52 (the last week in December). The year code would be 99 for the year 1999 or 01 for the year 2001. Commercial fabricators use a week/year format. Date code 0199 would be the first week of January of 1999. Military fabricators use a year/week format. Date code 0152 would be the last week of December of 2001. The printed circuit board fabricator shall place the date code on what is traditionally referred to as the circuit side of the printed circuit board.
What is the circuit side of a pcb?
To understand the term circuit side, you need to learn a little history of the printed circuit board industry. In the beginning (more…)
I had an interesting conversation with a colleague the other day. They wanted to return some printed circuit boards to an off-shore manufacturer because not all of the surface mount pads would solder. I help friends and customers troubleshoot problems all the time. Its just good business.
“Was it the entire lot of boards or only a few?”, I asked.
“Well, when we soldered the first batch the pads wet with solder with no problem. The second batch from the same lot has solderability issues. The pads don’t wet properly. I can’t explain it but nothing has changed here. The boards have ENIG on them so it must be the boards.”
“Well, if the first batch soldered and the second batch from the same lot didn’t then there’s a problem. How much time has passed between batches?”
“Hmmmm. About three years”
We then proceeded to have a conversation about shelf life. This is a topic that I find many people don’t know about or understand properly. Put simply, (more…)
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 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…)