Hello folks, I have a customer who has what appears to be very oxidized leads on a component. Their component mnf. has no new product to offer and they have 20K of these they have to solder to get product out the door. They are using a no-clean chemistry. The leads don't accept solder. I have gotten samples attempted the no-clean process with additional flux and higher temp to no avail. An OA chemistry with dipping the leads in OA flux and then tinning them in a solder pot and then testing the wicking of the lead with a solder iron works. Two questions: One is I believe I have removed the oxidation from the lead, however I know nothing of plating. If there is poor plating of the lead and I OA and then Tin is this acceptable? Will there be problems down the road? Second is we the clean the OA flux off the leads, populate the boards and send them thru a No-Clean process via Wave. Does this sound ok to do? Real hot issue if you can help would be greatly appreciated.
First, don�t get distracted by �OA� and �NC� formulations. This is nomenclature. We want to discuss the issue of �activity�.
J-STD-004 "Requirements for Soldering Fluxes" classifies fluxes by their chemical composition, activity level and halide content. Each flux type is identified by a 4-character designator. The first two characters are determined by the chemical composition of the non-volatile portion [i.e. RO for rosin, RE for resin, OR for organic, and IN for inorganic] of fluxes. The third character indicates the activity level: low (L), moderate (M), and high (H). The last character - 0 or 1 - indicates the absence or presence of halides, respectively. The combination of the last two characters describes the corrosive or conductive properties of the flux or flux residue. [Eurolanders have a standard (ISO9454-1) that is analogous to J-004. And it is very nice.]
But be careful, there is no absolute definition of activity in any of the fluxes. Flux vendors define activity levels [mg KOH/gram] and each of them has a slightly different concept of what is needed for a particular kind of flux. Complicating this, the difference between fluxes is less the amount of acid, than the strength of the acid being used. The rosin acids are very weak, and on the other end of the scale, some fluxes may even contain strong mineral acids like hydrochloric and hydrobromic. So, the mg KOH/gram is a meaningless number.
Taking this from a different angle, some activators, such as amine hydrochlorides, may be nearly neutral. These decompose at close to soldering temps, to release highly acidic gases, which would not be seen independently as acids during a KOH titration.
On to your questions �
Q1. If there is poor plating of the lead, is OA and then tin acceptable? A1. Yes, but as we�ve implied above, you could judiciously select a NC flux, apply it properly, reflow the components, and be good to go.
Q2. Will there be problems down the road [with OA and then tin]? A2. You need to remove the OA flux residues.
Q3. Does it sound ok to clean the OA flux off the leads, populate the boards, and send them through a no-clean process via the wave? Q3. Yes, but OA flux is not a prerequisite to removing the contamination on your component leads.
Consider talking to your flux supplier for recommendations.