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Surface Mount Soldering
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mikep



Joined: 24 Sep 2005
Posts: 771
Location: Austin, TX
Posted: 09 December 2007, 3:14 AM    Post subject: Reply with quote
dlh wrote:
There are formulations that have six-month life at room temperature - longer when refrigerated.
I would be interested in those as I use so little paste. My guess is that it is quite pricey compared to the usual refrigerated paste.

dlh wrote:
Sparkfun has a tutorial and links to a cheaper mylar stencil from a company in Las Vegas.
I don't doubt that stencils are useful but I think it comes down to a question of quantity.

For one-off thru-hole circuits I'm guessing most people use some kind of protoboard or stripboard to make a breadboarded circuit permanent. Perhaps at about 4 copies most people will want a PCB as the overhead costs start to make more sense. I find that only at about 25 copies does the PCB cost start to become reasonable. You can make your own PCBs but that has it own costs and problems are well. I haven't yet tried PCB pools like BatchPCB.com but that is a promising alternative.

The same for soldering. For less than 10 or 20 copies hand-soldering is probably sufficient. My guess is when you reach quantities of 20 or more then ovens and stencils start to become interesting.
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dlh



Joined: 15 Dec 2006
Posts: 287
Location: ~Cincinnati
Posted: 09 December 2007, 3:59 AM    Post subject: Reply with quote
mikep wrote:
dlh wrote:
There are formulations that have six-month life at room temperature - longer when refrigerated.
I would be interested in those as I use so little paste. My guess is that it is quite pricey compared to the usual refrigerated paste.

1 year refrigerated, 6 months at room temperature:
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victorf



Joined: 01 Jan 2006
Posts: 342
Location: Schenectady, New York
Posted: 09 December 2007, 20:15 PM    Post subject: Reply with quote
Check this out. 1 oz in real syringe with 23ga needle:

http://www.zianet.com/erg/ShopSolderPaste.html

21ga needles are available. The cost is $US5.00 each or 15 for $US60.00. 21ga needles are an extra $US1.00 ea. The smaller the gauge number the larger the hole

These will probably solve your shelf-life issues. Smile

HTH

Vic
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spamiam



Joined: 13 Nov 2005
Posts: 689
Posted: 10 December 2007, 17:14 PM    Post subject: Reply with quote
I will jump in here. I was very apprehensive about SMT soldering. I got a thermostatic soldering station (about $70) and 15mil solder. I use semi-paste solder flux that I apply by hand. I do not use solder paste due to expense. I would try an oven but my stuff is very much 1-off right now.

I have no problem soldering 0.5mm pin spacing. I would rather NOT do 0402 SMT resistors and caps. But 0603 is fine.

I use binocular loupes. I forget the magnification, but it is less than 5, I believe. Some higher mag would be nice to find the really small solder bridges. A 10x lighted magnifier on a stand would be a real help.

FINE point forceps are also critical to me.

I started using microcontrollers with the BX24. I took a pass on PICs and Stamps. When the ZX24 became available I jumped on it. I then used my good experience with the ZX24, and my limited experience in directly accessing the hardware registers to start using the plain vanilla AVR's (usually the ATMega128). 20 years ago I programmed fairly frequently in C for about 2 years, but after 1993, I did essentially no programming at all.

ZBasic is so structured that it is super easy to convert a ZBasic program into a C program (except multitasking). It is almost as easy as adding a semicolon at the end of each line in the program file!

The hard thing with C is the need to a multistage writing-compiling-downloading sequence. The compiling is a real pain in the neck when you need to use a "make" file. Expensive C programming software will take care of this for you.

Now Atmel's AVR Studio in conjunction with the FREE WinAVR C compiler will handle most makefile issues.

If you have never used C nor directly programmed an AVR chip, then I think that the most painless way to go is to use the Oak Micros OM128. Downloading the program is as painless as downloading a ZBasic program. If you use AVR Studio and WinAVR, that is quite easy too. I highly recommend this.

On my big breadboard I have a ZX chip and an OM128 next to each other. I can move the wires from a pin on the ZX to a similar pin on the OM128. I use the ZX for "rapid development" and when I get it working perfectly, I then translate the Basic to C and get the OM128 to do it. The only advantage is processing speed. Rarely is the speed the limiting factor.

What I usually am doing is a 3 step process. Development in ZBasic. Final development on the OM128 or another M128-based development board. Then place the code into a smaller device. Usually that device would be an ATMega48/88/168 because they are small and share the same footprint. I also use an ATTiny2313, but these Tinies have so little program space and I am so lazy with my code and variables that they do not fit. Additionally a SMT M48 has about the same footprint area as an 8 pin DIP.

-Tony
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