Soldering SMT parts
I've decided that it's time for me to learn how to work with SMT parts on circuit boards of my design. I'm thinking that with a bit of practice I can get PC boards designed with diptrace and have found a few places that make PC boards. My problems are many. The first is that I don't know what it is that the board makers will need to make the boards. I'm sure that a phone call to the pc board jobers will give me that info thogh so I'm not all that concerned.
What's got me scared is soldering the parts to the board. I've been looking at boards that have a prop, usb/serial converter soldered onto it and I have to admit that at my age my eyes aren't good enough to have a chance of getting the chip onto the pads of a board and touching each pin with a soldering iron without making a mess.
My question for those that work with smt boards is how do you place the parts onto the board and solder them into place. Any information would be greatly appreciated. If you live in the Chicago area I'd gladly pay for hands on help.
What's got me scared is soldering the parts to the board. I've been looking at boards that have a prop, usb/serial converter soldered onto it and I have to admit that at my age my eyes aren't good enough to have a chance of getting the chip onto the pads of a board and touching each pin with a soldering iron without making a mess.
My question for those that work with smt boards is how do you place the parts onto the board and solder them into place. Any information would be greatly appreciated. If you live in the Chicago area I'd gladly pay for hands on help.
Comments
I've not yet got started on this SMT thing myself, but there's been lots of good info on the forum for procedures involving toaster ovens, etc. Have you seen any of these:
http://forums.parallax.com/showthread.php?130196-How-I-do-SMT-soldering-in-toaster-oven
http://forums.parallax.com/showthread.php?128554-Soldering-Surface-Mount-Devices-at-Home
As a rough rule of thumb, you can get 15% positional error on your placement, and the surface tension of the solder will move it into place.
I use a regular handheld magnifying glass, as I can move my head,hand and PCB to get that extra magnification but still keep it in focus.
Sometimes I put on too much solder paste and have to use flux w braid to remove solder on bridged pins.
And I also use Hot Air SMD Desoldering Station to complete lift the IC off the board and start over on that part or at least nudge it in place.
Any thoughts on the type of toaster oven to get? I've seen references to model numbers but every time I check that model turns out to have been discontinued. Is there anything to watch out for when choosing an oven? I've also seen reasonably priced hot air smd stations and was thinking about using it to solder the parts instead of a toaster oven. Is that a good choice? My thinking was to use a magnifying lens to place the part with tweezers and then while holding in place solder it quickly with the hot air.
I would go for the oven instead of the hot air station (if you have to choose one). The oven has the following advantages:
1) It's faster: a complete board takes about 10 minutes total to cycle
2) You don't have to worry about moving the part (hot air stations may "blast" the part away if you're not careful)
3) You can do multiples at once
4) If you need to replace a specific part, simply heat it up in the oven and pull it off with tweezers when hot.*
5) You can do multiple boards at once.
6) You have more precise temperature control.
* Cycling the board too many times isn't good either. But a few is Ok.
Of course, if you get both an oven and hot air reword station that's even better.
I use this toaster oven. It heats up quickly and evenly, and is big enough to do many boards at once http://www.amazon.com/gp/product/B001L5TVGW/ref=oh_details_o00_s00_i00
That looks like a really nice oven. I can't tell from the Amazon site, though: are the time and temp dials encoders that produce digital steps, or potentiometers? ('Too bad one of the presets isn't "PCB" !
-Phil
The knobs are digital, and they are the kind the "click" when you rotate them. The one odd thing about the system is the step amount when you give fast rotations. Normally, when you rotate a knob fast it is slow for a little bit, then it starts taking bigger and bigger steps to get you there faster. But with this oven, it starts taking weird increments such as 6 or 13. It's awkward in a non-intuitive UI way.
But that's ok, since for my lead free solder I just put the parts on the top rack and set it to bake for 2 minutes at 230C. When it's done I open the door.
I selected that oven over other comparable 1800 watt convection ovens for two reasons: the quartz heating elements, and the digital controls. The first produces more even heat (I'm guessing), and with the second it should be easy(er) for me to drop in my own electronics if and when I need to.
The oven I currently use has digital temp control and quartz heating elements, but it lacks a convection fan. Consequently, I do not get even enough heating to do large boards.
-Phil
Sort of. I try to follow the Kaester standard solder paste reflow profile, which has a maximum temperature of 208-230C at a maximum time of 5 minutes. The oven actually takes a bit longer than that to heat up from a cold start, so it seems to follow the "Lee" profile: http://kicthermal.com/paper-a-articles/273-optimizing-your-reflow-profile-for-maximum-productivity-and-profitability
http://www.kester.com/LinkClick.aspx?fileticket=OUPpdDgnu4U%3D&tabid=181
Thanks everyone for you help. Now all need is a good and large magnifying lens. I have to admit I get the willies when I look at a board with a propeller and a usb/serial chip on it! I can barley see the pins let and can't imagine putting the chip in place. :frown: I'm thinking I'll need a 10x or 20x magnifying lens and when I'm trying to place the chips a shot or two to steady my nerves.
At some point, when I get some more time, I want to build something like the LPKF ProtoPlace E manual pick and place machine:
Basically, it has a vacuum pick and place and a nice work area with an adjustable hand rest. Unfortunately, it costs $1025. The Zephytronics vacuum is only $200, however, and I can build the rest of the PropPlace E assembly myself.
Anyway, that's what I use, and I've never had a problem placing small parts with it. For parts that are too large for the tweezers, one of these works just fine:
-Phil
Lawson
-Phil
With a metcal solder station I can do it with less issues. The difference between a good iron and anything else is impressive. I followed Leon's advice and I'm very happy with it.
You can solder 0805 passives with a relatively big tip. Even a uSD adapter can be soldered with big tips. The only tricky parts on a propeller platform style PCB are the propeller, the ft232, and less crytical the usb adapter and the eeprom (one side is usually all grounded).
For sure you need desolder braid, flux, and a nice solder station. Not less important are a support (panawise), tweezers and a magnifying tool.
Every manufacturer has different requirements, mainly on file names. I try to use trace and clearance way above the manufacturer's minimum in every situation.
Massimo
First board I've done (before and after toaster oven) here:
Have two different sets of precision tweezers and magnifying lens to get parts placed - very happy with the stencil frame though,
the PCB shop I use provides free laser stencils
The kind of solder paste placement I get is like this (different board) but sometimes have to redo if its smudged or pads are missing.
I set the toaster oven to "150C" nominal for a few minutes to prewarm and then full power whilest watching carefully - works nicely.
Since I've never had a PCB made it's my thought to call the company and discuss what it is they require from me to make a board.
Why call? There are numerous tutorials online on making a PCB in the software of your choice. Here is one for KiCad: http://teholabs.com/knowledge/kicad.html
In any case, the board houses are fairly standardized. They need gerber files for:
1) Top copper*
2) Bottom copper
3) Top Soldermask
4) Bottom Soldermask
5) Top Silkscreen
6) Bottom Silkscreen
And a drill file:
2.5) .drl
Every PCB house will have some sort of capabilities page, such as this one from Advanced Circuits: http://www.4pcb.com/pcb-capabilities.html
Just add some money, and you'll have a board in your hands in a few days.
-Phil
Mainly the layer naming convention, and the minimum sizes. Sometimes you have a predefined drill set too.
With Diptrace you can set the values in the DRC rules for automatic check.
If you are not in a hurry check services like Itead.
They are so insanely cheap that a test run cannot hurt.. :-)
Massimo
http://www.target.com/p/frigidaire-professional-6-slice-convection-toaster-oven/-/A-14036391#prodSlot=medium_1_1&term=6-Slice Convection Toaster Oven