Incrementally building SMD prototype - Page 1
Forum section: electronics / projects

author: markus_b
author_rank: Regular Contributor
timestamp: July 23, 2012, 07:25:31 am
content: I'm preparing the build-up of the prototype of my current new pet project (seeLab Power Supply discussion). I want to go carefully, checking for errors along the way, especially I want to verify the power and ground connections before soldering in the more complex chips (micro, op-amps). The problem is that it is all SMD with many small 0603 components.At the moment my plan is:- place solder paste on the pads of the small passive components (0603) and the 3.3v regulator, place the components, 'bake' the PCB in the family oven.- Supply power and measure the supply pins.- One after another, dispense solder paste, place a smd IC and solder it by heating with the hot air gunProbably starting with the microprocessor and the LCDAny better ideas or additional hints. This is my 1st SMD project of that size (80 components).Markus

author: joelby
author_rank: Frequent Contributor
timestamp: July 23, 2012, 07:57:58 am
content: Should be fine, and that's often how I like to do it when hand-assembling more complex designs.I would probably avoid using the family oven if you value your family, though. You won't be able to control the temperature as accurately or quickly as with a toaster oven or hot plate, or see through the window very well, and the flux fumes and lead will make your dinner taste awful.

author: markus_b
author_rank: Regular Contributor
timestamp: July 23, 2012, 08:09:34 am
content: The family oven is a good quality electrical appliance and it has a quite precise thermostat. It also has a quite large, clear window. As alternative I have a microwave/grill combo with the typical microwave window you can not really see through. The stove (vitroceramic) is also an option or an old two plate electrical stove with very uncertain parameters.I can also just solder everything using the hot-air gun, I'm just afraid the 0603 components get blown all over the place. Maybe I should perform some testing on a spare PCB first.

author: joelby
author_rank: Frequent Contributor
timestamp: July 23, 2012, 08:43:46 am
content: You're right - 0603 are a little bit tricky to do with hot air. If you've got a good eye or microscope and a steady hand (which you'll need to paste without a stencil and place components anyway), it's not too tricky to just solder them all by hand.If you're getting boards made by ITead or Seeed, you might find that you have plenty of spare boards so you can try a few different methods and see what works best for you.

author: Berni
author_rank: Super Contributor
timestamp: July 23, 2012, 08:51:21 am
content: I always just hand solder boards together. It doesn't look as nice as reflow soldering because its hard to put down all the passives down so precisely but it always works in the end. 0603 caps are easily hand soldered (0402 starts getting tricky but why would you use those anyway). Mainly cause i dont want to bother with stencils and don't have a spare toaster oven for reflow(hot air is not as nice)And yes i always build up a board in steps and power it up between them so i can first make sure my supply are ok and in case it stops working i can easily pin point the problem as it must have happened in the previous step. I had cases before where i messed up a resistor value at a switchmode and it made it give out 11V instead of 3.3V, would have been one hell of a bang if all the digital stuff was soldered down.

author: markus_b
author_rank: Regular Contributor
timestamp: July 23, 2012, 09:03:49 am
content: I've done as small 0804 board (10 components) this winter, this was before I had the hot air gun, so I just used my trusty Weller. This has worked out well.This project is *much* bigger in complexity and scope and I've changed to 0603 because there is more choice in components and of the they are cheaper. Also I've read remarks that 0603 is not really more difficult than 0804 to work with by hand. I've bought a SMD resistor and capacitor kit and found the components quite small. My eyes are no longer as good as years ago (getting 50 soon), but glasses and magnifiers help.I was just wondering of there are simple tricks to be aware of. One trick I've seen is that on qfp devices, like the op-amps, you don't need a solder paste dot per pin, but can just place a 'sausage' across all of them and the solder retreats from between the pins when melting. Of course I'll have to see how that works out for me in practice.

author: Rerouter
author_rank: Super Contributor
timestamp: July 23, 2012, 09:05:54 am
content: being i commonly have to rework boards filled with smd parts, i will say as long as your hands are steady its not that hard to handle 0603 hand soldering them if you get a bad bake,though not perfect, being how i commonly use a 1mm conical tip, is to at a moderate speed heat then swipe perpendicular across the pad/ edge of part, it generally leaves a near perfect joint, as the excess solder chases the tip off the pad,also good luck on the supply and i'll go over the filtering one last time on the schematics in the other thread,

author: Berni
author_rank: Super Contributor
timestamp: July 23, 2012, 09:46:58 am
content: Yes the 0604 do look tiny but as long as your PCB has nice big pads its just as easy as 0805. But you do need a good pair of smd tweezers(Ones that have a tiny and sharp tip) so you can grip the component easily without the tweezers being in the way of soldering.As for tips as Rerouter said remove the tip from the pad by swiping it sideways since lifting it up often creates a ugly spike of solder on top. Also applying fresh solder on to the joint fixes any spikes.I solder 0603 parts without magnification since im still young and have a good enough eye sight, for doing more fidely stuff like tiny 0.4mm pitch chips i often use a USB microscope to aid me. A proper optical microscope is very expensive and takes up a lot of space, but you can pick up these cheep USB microscopes all over ebay.http://www.ebay.com/itm/Supereyes-200X-Digital-Portable-Microscope-Otoscope-Magnifier-wLED-tripod-SALE-/330646720774?pt=LH_DefaultDomain_0&hash=item4cfc149106This is the one i got and it works great for soldering under it, its very small and comes with a tripod for holding it above your work area. The working distance is roughly 4cm at a magnification useful for soldering so with its small size its not in the way at all.Its quite convenient for me because i have a PC right next to me so i simply fullscreen the video feed from it. The quality of the image is pretty good for a cheep webcam with a macro lens on it and the video is a nice smooth 30fps when it has enough light.

author: T4P
author_rank: Super Contributor
timestamp: July 23, 2012, 05:06:57 pm
content: Quote from: markus_b on July 23, 2012, 08:09:34 amI know you either you do not have one in use, but are planning to get one from the supermarket or you plan on using one ...NO.Precise is the last thing you want to talk of a oven, they can go wildly 20C out of check, just because food doesn't need to be in within 5C ... But electronics do.What many people do is hack the oven to have a more accurate PID controlled oven, with a thermocouple and some uC

author: KTP
author_rank: Frequent Contributor
timestamp: July 23, 2012, 09:49:02 pm
content: binocular microscope, SMALLEST rosin core solder you can find, flux pen, (I like the Kester brand), needle sharp tweasers, and you can solder 0603, TSSOP, TQFP with no problem.flux pen and smallest dia. solder possible are key imo. A trick which works well for me to rapidly put down 0603 resistors is pen flux the pad, place resistor on it, hold down resistor with tweaser point, touch one pad with solder iron tip that has a bit of relatively recent solder deposited on it. I will tack down 10 or so 0603 parts like this, then reflux pen them all and proceed to solder first the other side, then resolder the side orginally tacked down, making all joints shiny and perfect. I can do about 100 parts an hour like this.