Hi There! Before I start, I gotta' ask, isn't Compeq a PCB fabricator?...and your customer is asking you how to implement their assembly processes? Like you haven't got your own problems, huh? Oh well, I suppose that's all a part of servicing your customers... Anyways, I'll just go down the list with your questions. At my last employer, I was responsible to convert us over to no-clean soldering. All we did was pure surface mount, no wave soldering, so as far as that aspect of it, there's others out on the list that have more experience with that. One thing that you don't mention is if they're already in a no-clean process or not. If they aren't and they're asking you how to implement no-clean, I sure hope they know that there's *A LOT* more to implementing no-clean than picking out a solder paste and throwing away the cleaners, A LOT MORE. Selecting the solder paste is the easy part, it's everything else that a no-clean process demands and requires that makes it quite a bit of work. Rework, ICT, Receiving Inspection, Purchasing, Material Handling, all are affected in a no-clean process. Another thing, if the existing assembly process isn't very well controlled, switching to no-clean is going to be pretty painful. That's the key, EVERYTHING about a no-clean process must be under good process control. With that being said, let's address your specific questions; > 1.What kind of no-clean solder paste is most compatible to Cu-106A? I evaluated pastes from three different vendors, SCM Metals, Qualitek, and Enthone. I don't want to say one is any better than the other, because they all performed acceptably. I had my own personal likes and dislikes, but he decision was made that included business factors and relationships (price) as well. The criteria that we had for the paste we used was; 1). It had to print well down to 16-mil pitch. 2). Reflow performance had to be good, good wetting, nice shiny joints, and that kinda' stuff. 3). The residue that remained had to remain clear during multiple reflow cycles and non-tacky since we routed out a lot of our products and didn't want to attract the router dust. 4). Of course the residue remaining couldn't cause any electrical performance problems and had to pass standard SIR testing. 5). The assembly also needed to pass temperature cycling for 500-hours, under power without failing. 6). We wanted a vendor that could provide a whole package of soldering materials to us, Paste, wire-core solder, and touch-up flux. That way we would have to go through a bunch of experiments finding compatible rework materials to use with the paste. > 2.What will the max. storage time after open bag to assembly? Is there any > concern to store in controlled environment ? Now supposedly, according to stuff I've read in NEPCON proceedings and the like, OSP coatings are better to, or at least equal to the storage life of HASL'ed or Gold Plated PCB's. High humidity is something to be concerned about because it will degrade the coating. That was somewhat of a concern to us because the company has a facility in Puerto Rico. But as long as you keep the PCB's sealed with a desiccant inside moisture-proof packaging, you should be good for at least 6-8 months...you don't plan on keeping PCB's on the shelves any longer than that do you? One thing that OSP coated boards have a problem with is handling. The coating is pretty fragile. You can't slide and stack them against each other without scratching the coating and exposing copper...then you DO have a problem. One other thing, I've seen boards from A LOT of PCB fabricators that have done the bed of nails testing AFTER the coating has been applied. You can see where the probes marks have pierced the coating. Excuse me if I'm missing something here, but ain't the whole point of OSP's is to seal the solderable surfaces from the air? Maybe I'm wrong...but I don't think so. > 3.Is it necessary to reflow in Nitrogen environment ? It wasn't for me, but we weren't looking at any REAL LOW residue pastes. There's some pastes that leave little, if any residues that are very low in activity that benefit from an inert atmosphere. But there's a lot of no-clean paste formulas that don't need nitrogen. > 4.What is the max. hold time between first and second IR reflow ? We would reflow one side one day, and do the second side the next day and not have any problems. So if ya' want a figure, I'd say 12-18 hours is safe, but that's with CU-106. The first time I used CU-56, you need to do the 2nd reflow within 4-hours...the quicker the better. > 5.How to rework bad paste printing like skip or misalignment ? That's easy, get yourself an ultrasonic stencil cleaner and clean your misprints in that too...it works great! > 6.Any other concern using Cu-106 A? Not that I can think of...I like the stuff! Nice flat pads, and it seems to cut down on bridging with the fine-pitch components because the solder volume for each joint is much more controlled. You don't have the plating thickness variances like you do on a HASL'ed fab, and the solder paste seems to stay right where it's been printed. Good luck, and make sure your customer doesn't blame you guys for their problems! (GRIN) B-) __\/__ . / ^ _ \ . |\| (o)(o) |/| #------.OOOo----oo----oOOO.-----# # Steve Gregory # # SMT Process Engineer # # The SMT Centre Incorporated # # [log in to unmask] # #________________Oooo.__________# .oooO ( ) ( ) ) / \ ( (_/ \_) *************************************************************************** * TechNet mail list is provided as a service by IPC using SmartList v3.05 * *************************************************************************** * To unsubscribe from this list at any time, send a message to: * * [log in to unmask] with <subject: unsubscribe> and no text. * *************************************************************************** * If you are having a problem with the IPC TechNet forum please contact * * Dmitriy Sklyar at 847-509-9700 ext. 311 or email at [log in to unmask] * ***************************************************************************