SMT prototyping/DIY reflow ovens

[forgie]

I've never done any SMT designs, and I'm wondering how many people here have, and how they've done it.

There's an interesting article in Elektor from December I think that details how they converted an old mini toaster oven into a reflow oven. Has anyone used this technique? Is there a better way to do cheap, fast SMT prototyping? Does anyone etch their own boards too?

Any tips, methods, experiences would be much appreciated. Thanks folks...

[eoasap]

i use SMD all the time. hand solder everything (qfp80, 603 resisters/caps, etc)

i have never used the toaster oven to solder (i know many have), but i have used it to remove an expensive qfp64 several times. works great! going from memory, most devices can't go higher than 430 F or so. Professional reflow ovens do a preheat/conditioning and then quickly bring everything up to optimal temperature and cool down. you'll want to read up on reflow stages and try to emulate them best you can if you plan on assembling boards that way. For my purposes (just taking stuff off), i preheat to 400F, stick board in for about 30 seconds, then take off my part before it cools down.

Keep in mind you should NEVER use a toaster oven for food after its been used for reflow. Also make sure to do it in a well ventilated area.

i've tried etching my own boards, i was turned off a bit by it for a few reasons:
1) you're dealing with strong acids and bases
2) trace width is higher than many fab houses
3) you still have to manually drill all your own holes/vias which sucks if you have a complicated board (or small vias)
4) no soldermask, so harder to solder high pincount surface mount

i go to pcbfabexpress to get my boards made, i end up with 5 boards for $80 (including shipping), includes soldermask and silkscreen

[sean-h]

I always found the re-flowing bit was the easy bit, getting the correct amount of solder paste on the PCB's is the trick.

In the end I purchased a air driven liquid dispenser:

http://www.intertronics.co.uk/products/cjbe1113.htm

This is great and dispenses the correct amount of solder paste on each pad.
Using it by hand takes a while but rigging it upto a cnc machine works a treat.
I need to update my site with examples of it on a machine when I get time.

After using this I was just using tweezers to place the SMT components, but again plan on using the CNC machine as managed to get a cheap pickup pump on ebay which will do small components.

For re-flowing I purchased a small roaster oven for around £40.00 that goes upto 250c and used this. But again on ebay picked up a small conveyor reflow oven for a couple of hundred pounds which does the correct pre-heat and different heat areas.
Problem is with Lead Free components now becoming the norm apparently you need more heat

As far as making PCB's have manually etched for years and used up plenty of caustic soda and wasted many a PCB board!!!

Best find was replacing the caustic soda with Seno PCB apllicators.
http://www.rapidelectronics.co.uk/rk...9438&XPAGENO=1

I wasted so many PCB's getting the mixture correct using commercial developer products as well as caustic soda LOL!
I have never wasted a PCB with these applicators and it also does not burn your skin off!!

Am trying to perfect milling the PCB's via the CNC machine now to do away with chemicals completley.

Regards

Sean.

[bartman]

I'm struggling with a small project that needs SMD parts as well. Mr. E sent me this link which I think is helpful if you are going to do it by hand:

http://www.infidigm.net/articles/solder/

I make my own boards because I never need the quanity to make it worthwhile to have them done professionally.

I use the laser printer method with the special toner paper then iron it onto my board. Once you do a bit of experimenting to get the iron temps right it makes a fairly clean transfer. Recently I started using the green film that is also made by the same company in addition to the toner transfer and that works very well. Makes nice clean lines and no etching pitting like there is with just the toner being the resist.

Bart

[forgie]

you'll want to read up on reflow stages and try to emulate them best you can if you plan on assembling boards that way.....

Keep in mind you should NEVER use a toaster oven for food after its been used for reflow. Also make sure to do it in a well ventilated area.

Yeah, the Elektor article has a uController based controller which follows a very specifically controller temperature curve. I'll try and rig up something like that I think. PCB manufacture may still be something to 'outsource'. Does anyone know of any cheap PCB fab houses that will send internationally? I'm in Australia, and all of the Australian PCB places have large minimum orders (usually a whole panel, which is about $300 AUD = $220 USD) which isn't practical for the home hobbyist/smaller project.

[eoasap]

batchpcb (sparkfun) has a deal where its a $10 setup fee and then $2.50 sq/in with no minimum requirements. i think its a great deal if you have a small panelization or single, small board you want to test. they also ship internationally. http://www.batchpcb.com/shipping.php

---- quote below from the link above---------------------------
International customers - read very carefully. We have shipped to over 85 countries and growing. We have had a 99% delivery rate with only 2 lost packages to Canada via Airmail. This is not to say it is fast. Some packages took 6+ weeks to arrive at their destination. Customs inspections and ground transport can take time, be patient.

* FedEx International Priority is very expensive ($40+) but is blazingly fast, 3 days usually. Trackable and insured.
* Global Express Mail is expensive ($20-$30) but is also very fast. 3-5 days, trackable, insured.
* Global Priority Mail is cheap ($10-$20) and is reasonably fast. 3-9 days, not trackable, not insured.
* Airmail is dirt cheap ($5-9), but is slow. 4 days and up, not trackable, not insured.

[forgie]

Thanks for the links guys. It looks like I still have many options for cheap PCBs after all, even being down in the other corner of the world!

[DynamoBen]

I etch my own boards, usually because I like to free up a bread board and am too cheap to keep buying dev. boards.

I've found it pretty easy and straight forward. For me it’s harder to create the PCB layout than it is to etch the board. I use the Press-N-Peel sheets, usually purchased through http://www.allelectronics.com/cgi-bi...OARD_KIT_.html. However recently I found out you can get as good or better results, with a magazine. You print the design with a laser printer onto a piece of glossy paper out of a magazine. Place that page onto your board and heat it with an iron (on the highest setting) the design will then affix it self to your board.
http://myweb.cableone.net/wheedal/pcb.htm

I started etching with the kit from Radio Shack but quickly out grew it. I now have a plastic tank with heater and pump.
http://www.circuitspecialists.com/prod.itml/icOid/4231

I use Ammonium Persulphate because it is clear so I can see the progress and can be purchased dry. (easier to store) I also tin my boards with "Liquid Tin." I originally used the stuff you have to put in the oven. It took the better part of an hour and stunk up the house. Liquid Tin takes five minutes, no heat required, very easy.

Finally, I haven't done SMT stuff yet. However the guys at sparkfun.com have done three tutorials on it. These are the techniques they use; my favorite is the skillet which works pretty well.

Enjoy:

http://www.sparkfun.com/commerce/pre...Reflow Skillet
http://www.sparkfun.com/commerce/pre...Reflow Toaster
http://www.sparkfun.com/commerce/pre...p?p=Stenciling

[O2_Guy]

Hi,
I've had experienced with SMT since the early seventies at MIT Lincoln Laboratory working with flat-pack 54 series TTL. I have to say, over the last ten years, everything, just about, I do in SMT. 10 years ago I tried etching my own; at the time I used TraxMaker for the PCB design, usually my prototypes were 2 layer and any hole plated-through. I found out, through the years that consistancy and repairability were always an issue. I also just plain never had the time to do the work. Now, remember, I'm talking professional R&D design and prototyping. I'm sure if I were doing it as a hobby I might not had gone the route I took that I am about to explain.
First, I generate the board layout from my design. I use OrCad schematic capture, so I generate a netlist for the connectivity and import that file into Protel's TraxMaker, now part of the CircuitaMaker Suite. I do the layout, check the output netlist against the input and when ok, I generate Gerber Files. I send the Gerber files to Advance Circuits; www.freedfm.com. The people do a design check for the hole clearances and traces etc for free. (DFM = Design For Manufacturing).They send me a quote and pdf files of all my layers. For prototyping, I generally buy quantity 3 for $33 each. With Shipping, that is usually about $119 US total. I then either hand solder the boards or order the parts through DigiKey.com or Mouser.com and have them drop-shipped to Advanced Assembly http://www.pcb-assembly.biz. They assemble my boards at a very reasonable cost and ship any parts overage back to me. I can literally finish a circuit design on a Monday and have assembled boards in my hands the following week on Wednesday..now that's quick turnaround!
Also, if you want to do the oven thing, get on to the www.freedfm.com website and order a stencil. You can then spread solder paste on the board, pop them in the oven and voila! Advanced Circuits (FreeDFM.com) has many good hints and good people to help you.

[Ron Marcus]

I've been working with "fun" (insert PIA) QLP packages for some Chipcon ICs. The website www.sparkfun.com has some great articles on reflow ovens, and using hotplates for smaller boards. I splurged for a $30.- solid element hotplate from Target, bought some lead bearing paste, and went to work. The first 4 X 3" board I did came out just O.K., so I shelved it and proceeded to make a break out board for the 20 pin chipcon CC1100. It took me nearly three hours to solder by hand, which included an hour of making sure all pins on the 1100 were attached.
For the second board, I decided to retry the hotplate. Learning the lessons of the first hotplate experience, I pasted, placed the components, fired up the hotplate, and had a complete board (working) in under 30 minutes!
I will never go back for SMT work...NEVER! With the amount of prototypes I make, this fits in nicely with all the other household items I have mutated for PC work. An oven with temp control would do well for items with heavier connectors that would needed to be heated from the top and bottom. Hmmm, that George Forman grill of my wife's does just that! I'll get back to you ;<)

Ron

[Luciano]

Baking Cookies.....

Luciano

[Luciano]

ALTERA
Reflow Soldering Guidelines for Lead-Free Packages.

http://www.altera.com/literature/an/an353.pdf

Luciano

[Luciano]

Circuit Cellar Magazine
Issue 168 July 2004

Easy Reflow
Build an SMT Reflow Oven Controller

http://www.circuitcellar.com/library...acoste-168.pdf

Project files: (Download Lacoste_168.zip)
(Inside the ZIP a PDF + basic source code).
ftp://ftp.circuitcellar.com/pub/Circ...llar/2004/168/

Luciano

--

[ScaleRobotics]

Sparkfun has a nice toaster controller here. http://www.sparkfun.com/products/81

I tried it for the first time a month ago, and it seemed to do very well. One thing I did notice when I hooked it to my Oster, is that for the cooling profile, there is no way that a toaster oven will cool down fast enough to follow the temp profile of Kester! What I did to keep the parts from getting too cooked is crack the door open and try to keep the actual temp close to the desired. Since these are displayed together on the LCD, this made it doable. I have not read anything about this being a problem in the couple of toaster oven write ups I have seen. Anyone else run into this, or solved it?

[mackrackit]

I may be doing it wrong..
I just use the temperature control that is on the oven with an oven thermometer (kitchen type) to monitor it. My oven also has a timer.

I set the temperature for around 350 F and the timer for 15 minutes. Place the boards in the cold oven. When the timer goes off I leave the board in the oven with the door closed. The slow cool down seems to have less oxidation than a fast cool down.

[ScaleRobotics]

I set the temperature for around 350 F and the timer for 15 minutes. Place the boards in the cold oven. When the timer goes off I leave the board in the oven with the door closed. The slow cool down seems to have less oxidation than a fast cool down.

Thanks Dave, I guess I could have saved some money then! Although I was making boards with rgb surface mount leds that are supposed to be pretty sensitive about being baked. Here is the profile for the solder I was using. They say optimum performance is below 5.5 minutes to peak temp, and show it in reflow zone for 75 seconds.



I notice most manufacturer's specs are quite short. Here is some info from Microchip.


But perhaps I am being too worried about cooldown. And just keeping the door closed would be more gradual cooling.

[dhouston]

I just use the temperature control that is on the oven with an oven thermometer (kitchen type) to monitor it. My oven also has a timer.

I use a small kitchen count-down timer. I have critical points marked on the temperature dial and make changes manually. Initially, I used temperature strips and a thermocouple but now just wing it as the manual methods seem adequate. The only problem I've had over hundreds of boards is with some large components (2.1mm power jack, RJ11 jacks, etc.) starting to deform. I now leave those for manual soldering. I usually have ~50in² of boards so just open the door after the brief soak at high temperature. My boards probably wouldn't meet ISO standards but none have exhibited problems.

I do use a stainless steel stencil for larger boards and for v-grooved small boards. It precisely controls paste thickness and I cannot recall a component misalignment with a stencil while manual paste application frequently results in misalignments that need manual resoldering.

I have a spinal cord injury that has paralyzed the fingers of my left hand. I use tweezers to place components. I design using 805 or larger components. I figure anyone should be able to do this if a one-armed geezer can handle it. I find it easier than manual soldering through-hole components.

[rsocor01]

Initially, I used temperature strips and a thermocouple but now just wing it as the manual methods seem adequate.

I think that using a non-contact infrared thermometer is the best way to control the temperature. Of course this is true if you don't want to spend thousands of dollars in a professional reflow oven. I bought this thermometer from Home Depot for under $30, and it works great!

http://www.homedepot.com/h_d1/N-5yc1...atalogId=10053

You aim the laser at the boards that you are "cooking" and it will tell you the temperature either in degrees Fahrenheit or Celsius. You can even see the difference in temperature at any given time between a metallic part in your board and a PCB non-metallic section in your board.

Robert

[kukata86]

http://www.kukata86.com/en/what-is-r...ven-controller