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Old 16th April 2007, 06:06 PM   #41
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Quote:
Originally posted by koolkid731
Is there a better way to solder SMD other than soldering on end and then soldering the other end? Does it pay to dispense solder paste then glue the SMDs on to the PCB, then pass it thru a "reflow" owen.

I use home owen to smooth out the solder joints but I wonder about the use of solder paste. Any wisdom out there?
1 Place fresh tin on both pads.
2 Place the part
3 Warm with TWO soldering irons, move them horizontally away. When the tin is melt the part will suck itself into place.

This is real easy you can can get an additional iron.
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Old 17th April 2007, 12:55 AM   #42
BWRX is offline BWRX  United States
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Quote:
Originally posted by koolkid731
What if I hit the boards and dislocated some SMDs? I would have to reposition them again, wouldn't I.

Why should one remove flux with isopropanol? for reliability? to prevent further chemical reaction? (acid attack?)
Paste can be a pain to dispense but if you can solder all the parts properly in one pass it's worth the effort. Normally parts stay in place fairly well unless you really whack the board or drop it. The tiny size and mass of SMDs means low inertia. You'd be amazed at how fast a pick and place machine operates at full speed and it just places the parts onto pads covered in solder paste without them falling off.

Some fluxes (and solders with flux cores) are designated as no clean, so you don't need to clean them off the PCB. Others can be toxic and even conductive if left on the board. Generally it just looks nicer if you clean the board off too. Here are a couple good articles to check out:
http://www.circuitnet.com/experts/EQ10123.shtml
http://www.logwell.com/tech/servtips/cleaning.html

As it says in the one article, cleaning flux with alcohol and brush is pretty worthless unless you remove the residue from the PCB. Lint free wipes such as Kimwipes are great for this purpose. Or you can find a good lint free resuable towel.
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Old 18th April 2007, 02:03 AM   #43
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If you get really keen you can etch your own paste stencil in 0.005" brass sheet. I did this when I had a bunch of the same board to make. Its actually very easy.
Reflow can be done in a cheap toaster oven - just stick in a thermocouple, and run up from cold to about 205C then turn off and allow to cool slowly. My workmate successfully soldered a small BGA device on a homebrew pcb using this technique.

The nice thing about reflow is you don't have to be too precise with component placement - the surface tension of the molten solder pulls everything nicely into alignment.
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Old 18th April 2007, 11:48 AM   #44
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Quote:
Originally posted by TwoSpoons
If you get really keen you can etch your own paste stencil in 0.005" brass sheet. I did this when I had a bunch of the same board to make. Its actually very easy.
Reflow can be done in a cheap toaster oven - just stick in a thermocouple, and run up from cold to about 205C then turn off and allow to cool slowly. My workmate successfully soldered a small BGA device on a homebrew pcb using this technique.

The nice thing about reflow is you don't have to be too precise with component placement - the surface tension of the molten solder pulls everything nicely into alignment.
Circuit Cellar had a toaster oven controller about 5 years ago -- this was surpassed by an article in Elektor with an oven controller which mimic-d the actual heating and cooling profile of the expensive reflow ovens. i just use a toaster oven purchased at a local bed and bath store and find it works well.

if you get your workspace and work-chair at the right level you can hand solder SOIC's and 0603's by tacking one end down -- i use a very, very fine pair of tweezers from Italy.
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Old 18th April 2007, 12:46 PM   #45
Nordic is offline Nordic  South Africa
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I am quite an avid follower of goings on on the head-fi forum....

I have seen many people remark how much better their smd projects ended up sounding compared to the same item in leaded format... I think the headphone setups are ideal for hearing subtle diffirences like that.

I have yet to bite the bullet and buy enough SMD components to actualy build anything, but I do intend to move to SMD just for extending the lifetime of my hobby... I think at some point leaded will be very scarce...
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Old 18th April 2007, 01:00 PM   #46
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Nordeek -- i like smt 'cause i don't like drilling holes -- my surface mount super regulator works as well as the through-hole version (I did buy the Old Colony boards to compare the two devices) and the SMT version is about 1/2 the size so it's great for retrofits. If you are going to burn your own boards it is very simple to do so with these components.

SMT components are cheaper -- you can buy assortments of parts from folks like Jameco, Digikey, Mouser and the tolerances are also better.

of course you won't find polystyrene caps -- these would turn into goo in an a reflow oven.
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Old 22nd December 2007, 01:19 PM   #47
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I was just on WIMA's website -- they now have a big range of polyethylene naphthalate and polyphenylene sulfide and PET. The cans get pretty big for the large values -- C6054

Here are max of the range for 63VDC:

PPS range to 470nF
PEN range to to 4.7u
PET range to to 6.8u
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Old 22nd December 2007, 01:57 PM   #48
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I now do lots of SMD soldering. I use solder paste and a toaster oven converted into a reflow oven. For prototyping, I apply the solder paste with a syringe and a fine tip. For production, I use a stencil and squeegee (from Stencils Unlimited).

I was apprehensive at first, but now that I have been doing it for a while, I definitely prefer SMD to through hole. For building, it is much faster. For repair, I use hot tweezers. Repairing through hole is not any easier. With hot tweezers, you just grab the smd part and lift it off. You can use them to put the new part on as well, then touch up the joints.

I do all my part placement by hand with tweezers. For ICs I sometimes use a $7 vacuum pickup pen, then nudge the part with the tweezers. I have a hot air station but haven;t used it for anything in a long time.

I am a bit mystified about availability comments. I find it is getting harder to find good through hole parts (apart from MKP and MKT caps). Take a look at Susumu thin film resistors at DigiKey. I am switching over to their RR series for almost all of our stuff (0805). We will be using 0.1% parts everywhere because they are so inexpensive.

Vishay has some nice 1% 2W power resistors too. Between C0G ceramics and Panasonic PPS films, I can get just about anything I need. Panasonic FK SMD el caps are the same as their FM through hole series.

Transistors and IC packages are generally identical parts, just a smaller package. There are cases where you run into thermal issues with the smaller packages, but that is changing. Look at Zetex and others, the power ratings are creeping up. If it's really an issue, just add a through hole part where you need it, and do smd for the rest.
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Old 22nd December 2007, 02:49 PM   #49
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I've used my "dedicated" toaster oven for MSSOP parts, haven't done any BGA but I am game to try this.

The WIMA SMD parts aren't yet available at Mouser, but I will call their US Distributor after the New Year and see where we can get some. They've been helpful to me in the past (anyone who needs the Wima MK2S-XL 10u/16V let me know by PM).
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Old 22nd December 2007, 03:12 PM   #50
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Here is where I got the oven controller: http://www.thesiliconhorizon.com/reflow.htm

Here are the hot tweezers I use (incredibly good deal as well). I use the tweezers attached to my hot air station but same thing):
http://store.sra-solder.com/product....d=6370&xSec=22

SRA has good deals on solder paste as well, though I got mine from Stencils Unlimited:
http://store.sra-solder.com/section.php?xSec=15
http://www.stencilsunlimited.com/sol...4a55eba1284ae8

I have been using the same syringe of paste for about 6 months now. I left if out in a warm room a few times and it started to separate, so I pulled the plunger out, stuck a tiny screw driver in and mixed it up. Been fine ever since. My New England basement workshop is generally cool enough these days to just leave it on the workbench.
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