New to SMT soldering

[digital_blue]

I've been doing standard thru-hole soldering for years now and I've decided to move onto the once seemingly impossible SMT.

What kind of iron is required? I'm not looking for anything fancy like a rework station and such... Should I be getting a simple adjustable temp station or would a regular "plug-in-wall" be sufficient? Would a 0.4 tip work for TSOP, SOIC and QFN stuff?

I have also looked into reflow soldering with an oven as a viable alternative to soldering the individual components. Are there any limitations to this method (frying chips and such)?

thanks

 

[JLSE]

Re: New to SMT

I recently started with surface mount boards. Its a bit of a pain but worth the size reduction. I use a basic adjustable soldering iron. I went to my local surplus guy and picked up the finest point tip I could find, and .015 super thin solder with resin core. I tried a surface mount project before getting the smaller tip, but it took way too long to assemble the board

link to that project - http://www.laserpointerforums.com/forums/YaBB.pl?num=1210808350/0

 

[rkcstr]

Re: New to SMT

A temp controlled iron would be good (one that actually monitors temp, not just "watts").

This one actually looks pretty nice for the price:
http://www.radioshack.com/product/i...&cp=2032058.2032236.2032313&parentPage=family

You just have to purchase extra tips online (the manufacturer is Madell, according to reviews).

As for reflow, that's what I do with the drivers I make and it works great. I just have a cheap counter-top oven I bought from Walmart. You just have to be careful of the temp, as most components say reflow no more than 260C for 30 seconds. My oven's settings peak around 200C, which works just fine. The settings on it are probably not entirely accurate, but more importantly, you need to follow a certain procedure of heating with four phases:

1. warm up, slowly heating the components up and drying the solder paste
2. saturation, bringing the paste to close to melting point
3. reflow, phase where you turn the temp up paste the melting point triggering reflow (should be almost immediate after the 2nd phase). Hold for 30 seconds.
4. cool down. I usually at this point remove the boards from the oven and quickly cool by lightly blowing on them (too hard and you might blow the components off if the solder is still "wet"), not just let them cool in the oven.

This is pretty much the routine I follow:
http://www.seattlerobotics.org/encoder/200006/oven_art.htm

Also, you must not be too liberal with the solder paste. Too much and things will tend to float around on the board during reflow, too little and you'll end up with poor bonds (mechanically and electrically).

 

[digital_blue]

Thanks for all the info guys.

What would be the easiest way to solder a "10SON" QFN package? Should I be using reflow or should I solder it manually? Also, what do you guys use to dispense your solder paste? From what I've seen, it's applied with a needle of some sort... I've also heard that flux can be made from violin rosin dissolved in isopropyl alcohol. Any truth to this?

thanks

 

[JLSE]

Thanks for all the info guys.

Also, what do you guys use to dispense your solder paste?

thanks

I use my index finger :-/ or the old dip the solder in the paste. But I dont use any other method of soldering other than a decent iron

 

[rkcstr]

Never tried a QFN, but some people here use them. I know IgorT uses a chip like that on his drivers, you could ask him how he does it.

As for reflow, I'm sure it would work. If the pins are small, you can just spread a thin layer of paste across the pads and it should conform to the pad shape when reflowed, though you should always check for shorts afterward (especially when using a PCB without soldermask).

For me, I use a syringe with a short, blunt needle tip. I typically use a 23ga needle, though it does get difficult to get out occasionally and requires cleaning. In the US, you can buy these items from here:

http://www.smallparts.com/

For flux, I would suggest getting an electronics formulated paste. NEVER use plumber's flux or any acid-flux! I particularly like the "rosin flux pen" I have from MG Chemicals. It's a thin flux that comes in a pen style dispenser with a fibrous tip which allows you to apply a thin layer where needed.

 

[JLSE]

The package for the chip im using is the 6 llp. It has no legs only small concealed pads. Its the small black IC in the pic below. I solder just fine with a fine tip, and regular paste. The only changes I had made, was to add extentions to the traces on the board where needed.

 

[lasersbee]

Nice clean job wannaburn... and only with an Iron...
Old school is a good thing. ;D ;D ;D

 

[JLSE]

It just seems less complicated this way
And the more you make, the less time it takes
It would be nice if these IC's had legs, I would be scratching my head a lot less