We introduced OSP finish on some of our products but now need to add some discretes at the end of the process. From my little knowledge of OSP, this is difficult.
We'll SMT the boards and transfer them to another site for further processing. At the end of this we need to add some 0805s or 0603s (I'm still working this one out). These discretes have Sn/Pb terminations. We need to hand solder these to some PTH pads which are OSP finished. The pads are on a 2.0mm pitch with no pin protrusion. This is my problem:
1. Can we hand solder these parts using Sn/Pb core solder wire ? 2. Is there a better alloy to use ? 3. Core flux or liquid ? 4. Do we have to treat the pads before soldering ? 5 Which component package is best, 0805, 0603, PTH axial, radial ?
Consider using a roll solder with a flux that well matches the residues you can accept to be remaining on the board when you get finished processing. Many people use a no-clean flux cored roll solder for such operations, because they don't want to clean the residues and NC flux residues are relatively benign.
Go to Circuit Technology Center [http://www.circuittechctr.com/guides/guides.htm] and look at "Section 6.0 Jumper Wire and Component Modification Procedures". It will give you some ideas about how to approach this. These are battle tested process that are included in the IPC repair and rework guidelines. [Thanks to Denny Ferry and the folk at CTC for publishing this great work on-line.]
Cuppla more comments ... * Component size is in part determined by the design requirements of the circuit you are working with. After that consider convience. Usually, bigger components are easier to work with than smaller. * Must solders used today are lead tin. I would expect that that's what's on your board now. Consider using an alloy that's similar to the one that's on your board. Further, the metal content of the solder has very little [nothing] to do with using OSP. Flux used is slightly more important. * We have talked about OSP on SMTnet. Check the Archives. Some OSP can take multiple heat cycles. Solding to your pads may not be a difficult as you thing. But then again, it may be, and you may need a flux with attitude. * There are hundreds of Sn/Pb alloys used in soldering today. The most common are eutectic [63/37] or near eutectic [60/40]. * If you use a liquid flux, the raw liquid flux is going to going to be all over your board by the time you're finished and you should find a way to remove it, even if its a NC. Flux pens are handy for rework operations. They are sold by major flux suppliers and tool suppliers like Technitool. * As far as soldering a SMT component to a PTH goes, consider soldering a wire in the PTH and then soldering it to the component. * Your discussion of pitch doesn'r 'click' ... just can't picture your board.