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Eric R
10-11-2006, 09:28 AM
I would like to include the QFP in one of my projects due to space. The board will be made by Express PCB and I will likely spring for the solder mask. I found a couple old boards laying around with a similar chip and tried my hand at soldering. Needless to say it was tough and even tougher to clean up a short.

What is the trick or the best way to go about mounting this.

Is there anywhere one can be mounted?·(As in a business that provides this service on a small run basis reasonably?)·

Phil Pilgrim (PhiPi)
10-11-2006, 10:21 AM
Eric,

I've soldered the QFP using a syringe of solder paste with an RMA flux (from DigiKey) and a small infrared (for quickest thermal cycling) toaster oven. You can try to put a thin line on each pad or just lay a bead across each row of pads. Both ways work fine -- even without soldermask. Then accurately position the part on top, bake at 285 F for 2.5 minutes, then 460 F for 30 to 60 seconds. Open the oven right away when it's done so it can cool quickly. There will be some cleanup to do afterwards -- solder bridges especially. But that's what solder wick is for, and it works great. Get the good stuff with an active flux, not the cheap stuff that Radio Shack sells. Work quickly: you don't want to suck all the solder off. Inspect to make sure you can see a solder fillet between each pin and its pad. If not add a little spool solder with a hand iron and wick again.

Hand soldering is not out of the question, either. Be sure to use an iron with a built-in thermostat and a pin-point tip -- again not something you get at Radio Shack. Use a very fine, cored solder. The trick is to position the part accurately for the first two or three solder joints. This could be accomplished with cardboard fixtures taped to the board at each corner to hold the chip in place. Once you've got the first couple joints, position the iron and solder at one end of a row of pins and move slowly across it, staying just ahead of the molten solder. Don't worry about solder bridges. You'll clean those up later with the wick.

When you're done, clean the board with an old toothbrush and 99% isopropyl alcohol from the drugstore (not rubbing alcohol, which has too much water in it). You'll be amazed how clean and professional your results will look.

Good luck,
Phil

parts-man73
10-12-2006, 01:16 AM
I remember a reply that chip gave to a similar question a few months ago. But I couldn't find it now using the forums search engine. There was a short video clip, and I believe it was a water soluable flux. They made it look easy. If anyone else can find that thread, I'd apprieate it, I myself want to solder a FTDI USB chip to a circuit board. I just got my board back from the board house. But haven't got the guts yet to try to solder it. It's a 28 pin SSOP.

There's also a surface mount soldering tutorial on Sparkfun.com that you may want to check out.

But if someone can find that post from chip with that video clip, I'd really like to see it again.

Thanks,
Brian

Paul Baker
10-12-2006, 01:44 AM
Brian,

Are you refering to this video: http://www.howardelectronics.com/xytronic/Images/Drag%20Soldering%20107.wmv

The issue with the QFN package is the ground plane under the package. This needs to be soldered to a corresponding pad, but this is inaccessible via a soldering iron, so using reflow or a hot air pencil is nessesary. I have contemplated trying a hand solder method where there are via's in the pad and try to heat it using the vias·from the other side of the board, but I haven't tried it.

Most companies who will populate a small quantity of boards (for prototyping), will charge an arm and a leg. This is because most of them use pick and place machines and the time to setup the machine is a constant regardless of how many boards are made, so there is no amortization of the setup cost when producing a few boards.

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Paul Baker (mailto:pbaker@parallax.com)
Propeller Applications Engineer
[/url][url=http://www.parallax.com] (http://www.parallax.com)
Parallax, Inc. (http://www.parallax.com)

parts-man73
10-12-2006, 03:07 AM
Yes, that's exactly the video I was looking for. Just couldn't "massage" the search to find it.

I've got the chip and the board. Now all I need is that water soluable flux, and courage, and I'll try it.

More and more chips are being offered in surface mount only. I've resisted up to this point, but it's time. I just ordered a bunch of 1206 resistors and capacitors and that FTDI USB chip. We'll see how it goes.

Brian

Phil Pilgrim (PhiPi)
10-12-2006, 04:20 AM
One thing the movie doesn't show is how the chip is held in place before it's soldered. With it just sitting on the board, it wouldn't stand a chance of staying put during that operation. I suppose you could use super glue or double-stick tape, so long as it's thin enough not to raise the pins above the pads. I've never used either one, so wouldn't know what to recommend.

-Phil

Graham Stabler
10-12-2006, 05:33 AM
You can get hairclips that work a bit like crock clips, it is easy to modify one into a component clamp (use the basic mechanism but only one jaw), then ends can be filed to a point for holding even 0603 and the like.

I might have a picture somewhere

Graham

Eric R
10-12-2006, 08:20 AM
Thanks guys,

Now, do I need solder paste or·water soluable flux? I assume it is water soluable flux in the video. Would this then require water soluable solder also?

parts-man73
10-12-2006, 08:52 AM
Eric R said...
Now, do I need solder paste or water soluable flux? I assume it is water soluable flux in the video. Would this then require water soluable solder also?


Paste or flux is preference, I'm sure it could be done either way. I think the water soluable flux and drag method looks the easiest. I've followed threads in other forums describing how to modify a toaster oven to cook your boards, or hot plates even! http://forums.parallax.com/images/smilies/freaked.gif

As for you question about water soluable Solder. No, solder isn't water soluable (meaning it dissolves in water)

Brian

Eric R
10-12-2006, 09:33 AM
As for you question about water soluable Solder. No, solder isn't water soluable (meaning it dissolves in water)



I was asking because of digikeys number·KE1303-ND Organic Water Soluble Solder. I didn't know if both needed to be used together or if regular solder was acceptable.

bambino
10-16-2006, 10:44 PM
Eric,

As for holding the chip in place I have had success with the paper glue sticks that office depot sells(just let it sit overnight to harden). Be carefull with super glues and epoxies as they can release toxic vapors when you start to soldier.

Paul Baker
10-17-2006, 12:41 AM
Bambino, normal adhesives can't be used with QFN packages. The underside of the chip must be soldered as well, placing glue underneath will interfere with the connection. However, your advice has sparked an idea, this may be an excellent application for silver based conductive epoxies.

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Paul Baker (mailto:pbaker@parallax.com)
Propeller Applications Engineer
[/url][url=http://www.parallax.com] (http://www.parallax.com)
Parallax, Inc. (http://www.parallax.com)

Phil Pilgrim (PhiPi)
10-17-2006, 12:53 AM
Paul,

'Beg pardon, but I think he was talking about the QFP. Maybe I've made a wrong assumption, but all my comments in this thread, at least, have been directed to that package and not the QFN.

I've tried soldering QFNs, but with zero success. Since they're so hard to prototype with, I avoid them in my designs.

-Phil

Paul Baker
10-17-2006, 01:08 AM
You're correct Phil, somehow I missed that when originally reading his post.

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Paul Baker (mailto:pbaker@parallax.com)
Propeller Applications Engineer
[/url][url=http://www.parallax.com] (http://www.parallax.com)
Parallax, Inc. (http://www.parallax.com)

ALIBE
10-22-2006, 06:04 AM
another article that talks to surface mounting technique

http://www.sparkfun.com/commerce/present.php?p=Reflow%20Skillet#Hot%20Plate%20Reflo wing

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ALIBE - Artificial LIfe BEing. In search of building autonoumous land robot

http://ALIBE.crosscity.com/ (http://ALIBE.crosscity.com/)
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