 Notice. New forum software under development. It's going to miss a few functions and look a bit ugly for a while, but I'm working on it full time now as the old forum was too unstable. Couple days, all good. If you notice any issues, please contact me. |
Forum Index : Microcontroller and PC projects : uMite Reflow oven
  Page 2 of 2 |
|||||
| Author | Message | ||||
Grogster Admin Group  Joined: 31/12/2012 Location: New ZealandPosts: 9066 |
Just in case you or anyone else is wondering - I would have used the SPI device talked about on this thread earlier, had I known then, what I know now(ain't that always the way!). For this version, the AD595 is the thermocouple interface. In some ways, I like it better, as all you have to do is read an analog voltage - no SPI or I2C or other digital comms to decipher, although, I can see the logic in that approach. I have the PCB's for my controller, but I have not yet written and control code - that's next. I plan to use the VT100's nice big fonts to make an easy-to-read video display with menu etc - kinda like the thing you linked to - and the EEPROM can be used to store and read back solder profiles etc. ...a work in progress, there just never seems to be enough time to finish them all AND do your day job!  Smoke makes things work. When the smoke gets out, it stops! |
||||
bigmik Guru  Joined: 20/06/2011 Location: AustraliaPosts: 2870 |
Grogs, Did you get spare PCBs? I would be interested myself. I have a couple of questions though.. Do you need to get Stencils for solder paste? How do Ovens go with the Plastic (eg of header strips)? Regards, Mick PS. I would have preferred a 20x4 LCD display as VGA displays are either too large or too pricey. Unless there is an RCA composite output that I cant see there, in which case I think it is understandable why you went video instead of LCD display.. Mik Mick's uMite Stuff can be found >>> HERE (Kindly hosted by Dontronics) <<< |
||||
| Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9066 |
Yes. Probably. That is the best way to apply the paste. There is a place that makes cheap and quick mylar stencils, but I forget where - Dave of EEVBLOG fame talked about them in one of his videos. What was good about them was that you could get the stencil seperate, so having made the boards, if you later decided you would have liked a stencil, you can use these guys. I will see if I can find the video and link to the place Dave was talking about. They don't. In my case, I never planned to solder thru-hole parts with a reflow oven, only the SMD. That done and the board cooled down, you then manually fit and solder the thru-hole parts. If the board is 95% SMD, then there is not much thru-hole stuff to fit. Upper right-hand corner of PCB - VIDEO output. This is the composite video output, but the VGA output is also available. You are quite correct about size and cost for a VGA monitor, but the plan always was to use one of those very cheap composite displays you can get on eBay for $50 or less. Smoke makes things work. When the smoke gets out, it stops! |
||||
| viscomjim Guru Joined: 08/01/2014 Location: United StatesPosts: 925 |
Grogster, I hate to say it, but you have a bit of a chicken and egg problem. You designed your reflow oven controller with surface mount parts, but you need the working oven to solder it but you can't because the oven doesn't have a controller. How are you going to get out of this one???? JK of course. |
||||
MicroBlocks Guru Joined: 12/05/2012 Location: ThailandPosts: 2209 |
Whenever you have a chicken and egg problem you need a rooster. :) Very interested in the thermocouple use. Maybe having a look at some 3d printer schematics can help. Lots of them use thermocouplers and they are often used with Arduinos. Maybe some pages on the reprap wiki can help. Microblocks. Build with logic. |
||||
| Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9066 |
I'll send the PCB to you for soldering, then you can send it back. 
Seriously, i've already built the first PCB by hand, and am pretty used to SMD soldering by hand now, so it did not take long. Future boards can be via the oven. My only REAL concern with home-made ovens like this, is double-sided PCB's with SMD on both sides. One side done, if you flip it over to do the other side, whats to stop the first layer's SMD unsoldering itself as you try to solder the other side's SMD? Not sure about that issue - have yet to think of a way around that, as I often design with SMD on both top and bottom layers these days...... Smoke makes things work. When the smoke gets out, it stops! |
||||
| paceman Guru Joined: 07/10/2011 Location: AustraliaPosts: 1328 |
Very good point Grogs. I reckon they'd have to use an adhesive - high temperature capable at that. I've seen videos of surface mount boards being made with a pick and place machine where they first used the machine to put a dab of glue under each component before they were placed. I wondered why that would be necessary given the use of solder paste, stencils and ovens, but maybe that's why. Greg |
||||
| MicroBlocks Guru Joined: 12/05/2012 Location: ThailandPosts: 2209 |
The easiest way is to have light weight components on one side. They will be held in place by the surface tension of the solder. Small resistors, capacitors etc.. will stay in place. Bigger (heavier) parts that can overcome this surface tension can be placed with a tiny bit of epoxy. If you want to be really fancy you need IR heating to finely control the temperature so that only the top reflows. A silicone mat that can stand the temperature can be used to place the PCB upon. You would need to adjust how the air circulates to make sure the PCB gets hot enough. A silicone 'rubber band' can also be used to hold parts in place. Microblocks. Build with logic. |
||||
| paceman Guru Joined: 07/10/2011 Location: AustraliaPosts: 1328 |
That's interesting TZ, I wondered about a compressible mat of some sort - I was thinking maybe ceramic fiber cloth like used in kilns etc. I reckon for the sort of one-off or low volume stuff we all do a combination is probably the way to go. It's likely we wouldn't want to be restricted to just very small components on the bottom (think coin cell holders, USB sockets etc.) so a tiny dab of epoxy would be a simple solution - I wonder if Superglue (isocyanate) would work? I'd think if you were getting serious about it then a hot air soldering "iron" would be a big improvement too. One of the hassles I find with doing even 1206's, certainly anything smaller, is them "sticking" to the solder on the iron when you dab it on. Even if you are holding it in place with something pointy you've got to be very careful you don't move it. Greg |
||||
| Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9066 |
I've had that problem(1206 sticking to the iron) all the time, so yes - you have to hold the part there while you solder the first leg or pad. I use the smallest jewellers screwdriver flat-blade I can find. The other method I have recently adopted is to let the surface tension work in your favour with 1206. Put flux on both pads and place the part. Put a little solder on the iron, get yourself lined up, and go in with the iron to solder with the iron as horizontal to the part as possible. Once the solder flows, pull the iron away sideways at a low profile(NOT upwards or up-and-out) to the component, and the 1206 stays put, and when the surface tension breaks between the 1206 and the end of the iron, the part springs back to the centre of the pad, and this allows for near perfect alignment. This method does not require that you hold the 1206 at all - the surface-tension positions the part for you. There is a trick to pulling the iron away, but I think I have mastered it now. If you pull it away to slowly, the 1206 comes with you. If you pull it away too fast, the part can move too much, and the solder sets before the surface tension has pulled the part back to the centre of the pad. Smoke makes things work. When the smoke gets out, it stops! |
||||
| Page 2 of 2 |
|||||
 Print this page |
