Projects/PCB/Halogen reflow soldering



Alan (folknology) and Paul (plett) have had some luck with soldering surface mount components using a Halogen oven, specifically this one. It is in the space if anyone wants to use it.

Below is Alan's email to the list. This needs reformatting to be more wiki-like and less email.

As you may be aware from hackspace events page I                                                                                                                 plan on running and introduction to building Surface Mount electronics. Having used a number of different techniques and tools to work with SMD components I was keen to get something up and running at the space. Last weekend when ordering something from Maplin I noticed a special offer on                                                                                           this Halogen oven And decided to take a gamble and buy with the express purpose of using it                                                                                          to reflow smd pcbs. Having used toaster ovens and such before to do my SMD cooking I was interested in this device for 2 main reasons, 1 that it was halogen based and 2 that it is glass all the way around giving great visibility inside. Having great visibility is really useful and can be a                                                                                           pain with toaster type ovens and is mainly why I use a hot plate more frequently, thus this design represented a good improvement in terms of                                                                                            oven hacking. Last night along with Paul (plett) I decided to test the new purchase in                                                                                           the Hackspace. we performed a number of tests and were initially worried about the internal fan blowing small components around as it seemed to                                                                                             create a vortex inside. After experimenting we found that some areas were less prone to movement than others, we next moved onto heat tests with a                                                                                           small dummy pcb board and some solder paste. We tried at several different positions in the oven but struggled to get the board up to temp for proper reflow, in most cases we were on the edge of its performance. At this point we scratched our heads as to why a 250C degree oven wasn't getting hot enough to melt 180C solder paste. Finally we partially disassembled the heating section and removed the diffuser in the hope we would gain more focused radiation on the board rather than just air flow heating. Straight away the oven performed as expected with reflow happening around 180 giving us plenty of headroom for smd reflow (even possibly lead free). We                                                                                                 therefore decided to test a small real world PCB assembly that I had spares for and it worked perfectly first time, the results were excellent. Operation of the oven is very simple (although we will probably tune the                                                                                           recipe) its as simple as placing the pasted PCB on the high wire mesh stand inside the oven, centred. Next Set the timer for a few minutes, keep the carrying handle high (this disables the oven) set the temp to 150 for the soak target and press the handle fully down. The oven will engage, lights will come on and it will heat up towards 150C. Whe it reaches 150C the heating light will go off along with the halogen lamps you then start a                                                                                            stop watch (or count in your head) for about 10 secs (to be tuned) this allows the pcb and components to soak and fully warm. then wack the temp up                                                                                        to full and carefully watch your PCB. Shortly you will see the solder paste start to bubble and move from dull to shiny. Often components will move and align themselves onto the pads as via surface tension. When you are sure that all pads have reflowed (some reflow before others) take the temp back down to zero and carefully move the lid slightly to one side to allow the hot air to escape and the oven to cool more quickly. When everything is                                                                                            cool remove the lid and stare in wonder at your reflowed smd PCB, if your really brave stick it under the stereo microscope and inspect for issues, you will probably find near perfect joints as we did last night. I intend leaving our new Hackspace reflow kit at the space so anyone can use it whenever they wish, there is also small jar of solder paste in the fridge upstairs for folks to use and experiment with please help yourselves but make sure you don't leave it open and always put it back in the fridge, that way when the next hacker comes along to do some reflow the paste will still work nicely. It also goes without saying that if you intend using this equipment please be very careful its an oven and it gets very hot, it                                                                                         will burn you or someone else if you do not treat it with respect, thus make sure you are careful with it and make sure the people around you are aware of what's going on, that way hopefully nobody gets burnt. PS it stays hot for a good will after, taking the lid off and placing it                                                                                           upside down helps accelerate the cooling, but make sure you have plenty of                                                                                          room to perform the manoeuvre. Things still to do: 1) It would be handy to have some oven gloves for working it.                                                                                                      2) We will need to tune the timing for leaded and lead free. 3) I would like to add a small lcd stop watch on top of it, anyone have                                                                                            such a thing kicking about?                                                                                                                                         4) We still need to do some work on creating our own stencils (I used one I                                                                                         already had) using the laser cutter. we need some Kapton sheets to                                                                                                 experiment with perhaps someone can help with sourcing that? 5) I also need to get some bits together before running the SMD reflow class                                                                                       6) I would also like to find a better position for the oven and a longer lead as it was a little award where we tested (on the drill bench area) Anyhow a giant step for hacking kind and happy SMD hacking in the meantime