OOPs, I misspoke. I wrote: " I dip the wick in some good quality rosin solder..." I meant "I dip the wick in some good quality rosin FLUX..."
Ron AC7AC -----Original Message----- From: elecraft-boun...@mailman.qth.net [mailto:elecraft-boun...@mailman.qth.net] On Behalf Of Ron D'Eau Claire Sent: Thursday, April 19, 2012 2:23 PM To: 'Elecraft Discussion List' Subject: Re: [Elecraft] SMT and the K3 - Nerves Keep in mind that all of the step-by-step procedures in the Elecraft documents were actually done by the writer, tested by others, and then refined and improved by customer feedback. That's in accordance with Wayne's basic requirements for Elecraft manuals. So if you take the time to follow them closely, you are getting the benefit of the experience of a great many others who have been there before you. I have removed hundreds of two-terminal SMDs both by cutting them in half or by unsoldering one end at a time and lifting the part with never any damage to the pcb. At least some techs at Elecraft use this approach too. Deciding which approach to use takes a little thought about the type of SMD. Some chokes have very thick bodies that can be hard to cut. The danger there is more about slipping and damaging a trace or adjacent component than damaging the pads. But chokes conduct heat very well, and the solder at the opposite end will be softened if not melted making it especially easy to heat one end and at least lift the part up if it doesn't fall off completely. Low value resistors will act the same way. Unless someone has manually reworked the board, only a very thin film of solder is connecting the part to the board in any case. You know how easily your fine wire solder bends, consider how easily it would bend if flattened to an extremely thin foil. In most cases, that's all that is bonding the part to the board. All that's necessary to remove the component is to lift one end slightly to break the bond at one end, then do the other. So, if a part feels stiff as you lift it, go no farther than that. Even so, you'll find that most components will pop straight up with almost no pressure when one end is unsoldered. Be aware that some small components are glued to the board in the manufacturing process before they are soldered. They may take a little more "persuading" but it still works. (I've not encountered that in any Elecraft products.) Resistors and capacitors are much smaller and easy to cut with sharp cutters but I prefer heating and lifting when possible. I prefer solder wick for cleaning pads and removing excess solder from joints some over-zealous tech flooded with excess solder. I dip the wick in some good quality rosin solder before applying it with my iron set at about 800F (to compensate for the heat sink effect of the wick). The added fresh rosin makes a HUGE difference in how efficiently even the most expensive wick pulls up solder. My vacuum de-solderer is used only when cleaning out plated through holes. Success working with SMDs requires the right tools. As a minimum, you want a temperature-controlled (and ESD safe) soldering station with a very fine tip. I use a tiny spade tip (1mm) or a conical pointed tip for really small stuff. Some good tweezers are a life-saver, but I never use the spring loaded or locking forceps type. They easily launch an SMD across the room. I use the type I must squeeze and then work with the least pressure needed. I put the SMD in about the right spot, slide in into exact place and then hold it down for soldering one end, often with a wooden toothpick. You don't need more than two hands. Just hold the part with one hand and then touch your iron to your wire solder to pick up a drop and carry it to one end of the SMD. Use the tiniest drop possible. I talked my dentist out of some tools he no longer wanted. Most dentists replace their tools regularly. Some dental picks and hoes are great for manipulating tiny parts. Good light and your favorite magnifiers (if needed) to see clearly are essential. Of course there are those who invest in multiple point soldering irons special SMD holding jigs, etc. They speed up the work a lot but are not really needed for casual building or rework. At the other extreme you can get away with very simple tools. I've sat cross-legged on the deck of a ship rolling at sea holding a pc board between my knees and replaced SMD's using a butane-powered soldering iron and done it successfully, but I don't recommend it for myself or anyone else if there's any better tools or work space available. New techniques take practice but you will be successful the first time by simply following the recommended procedure, paying attention and taking your time. 73, Ron AC7AC ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
