-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 source= http://www.piclist.com/piclist/2004/01/12/200703a.txt? Austin has an active hi tech sector, so I can go over to M.C. Howard's and buy obsolete but new, empty circuit boards for a dollar or so a pound. I can also buy resistors by the reel, but sometimes these have a little oxidation on the leads. This makes the penalty of a catastrophic soldering failure a dollar or two, not $35 to $100. Always practice where you can bear the cost of failure. My current project is the first large soldering I have done in 20 or 30 years. I'm pretty pleased, since one of the Friday afternoon consultants says that I'm doing quality similar to a NASA level 3 solder tech and he would hire me in preference to his current tech. All of my lab background tells me to be consistent with what I do. If I am consistent and wrong, I have enough control to correct things. So I have been attentive to process details. I have the Radio Shack OEM (Clone?) of the Weller 25W iron. I don't know if it is thermostated or not. I notice that the first pin takes longer to solder (6-8 seconds) if I start with cold solder. If I tin and wipe the tip after any significant break, the solder is warm and the first pin goes at the same time as the others. Also, I have made my boards so that Pin 1 on the IC has a square pad. I solder Pin 1 last, not first, so as not to break the rhythm. I wipe the tip and inspect with a hand held loupe every 4 to 6 pins. For a small DIP socket, I may do one entire row before inspecting. Inspection is only a 10-12 second break. It would be better to have one of those 12" lenses with a circular fluorescent all nicely counterbalanced, but I don't have that at the home based lab. I marked a spot on the solder with wire cutters a few inches back from the tip, and measured the solder length before and after a 40 pin dip. I have not had access to an analytical balance, but when I weigh a length of solder, I have enough information to report what mass of solder I use, in average, per pin. This is approximately 1mm of solder per pin with the diameter of solder at hand. My eyeball estimate is that I use 20 to 50 mg per joint. This seems like the sort of thing that would be specified deep down in some government specification. I find that large pads are much easier to solder, but don't appear to consume any more solder. As to the time, with everything clean, it takes approximately 4 seconds per pin. This varies a little bit with gold plated machined sockets or resistors with long leads still attached. Gold is just beautiful to solder. It may be worth having gold plated sockets to save in the soldering labor cost. On leaded components, I have two styles. The leads are trimmed after soldering in both styles. In one style, I tin the iron, and use the melted solder to insure good heat transfer to the lead. I touch the lead almost 8-10 mm from the board, and touch the solder to the junction of the board and lead. I suspect that this puts a lot of thermal load on the component. In the other style, I use a wiped tip and touch the wire to board junction directly, with the angle of the tip flat against either the wire or the board. I touch the solder to the junction across the wire from the iron. I am not in good control on the character of the joint on the component side. Some of those joints have a meniscus, and others have not reached the melting point. On practice, I have held the heat for upwards of 20 seconds, and have put 3 to 4 times the normal amount of solder on some joints, without obtaining melt or meniscus on the component side. I don't know if this indicates contamination inside the thru hole. This is in a setting where other, apparently identical joints form the meniscus easily. Other failures I have seen, though rarely, are when the solder beads up on a lead, and does not form a meniscus with the hole on the solder side. I think this may be a problem that more flux will cure, and I have bought a bottle of resin in isopropanol. I will try to paint a stripe of resin on the sockets on the next solder job, and see how that goes. - --- Aubrey McIntosh http://www.piclist.com/member/AM-vima-Y84 PIC/PICList FAQ: http://www.piclist.com -----BEGIN PGP SIGNATURE----- Version: PGPfreeware 7.0.3 for non-commercial use iQA/AwUBQAa52wKlSw8yssF7EQLFOgCfSJYORVVB8Du+PTjj2oKsZSu54ToAniDR ujrQKdjzyJ8ztHkCnkqp6ZQU =y1TK -----END PGP SIGNATURE----- -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email listserv@mitvma.mit.edu with SET PICList DIGEST in the body