Solder Paste, Skillet, problem...

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I managed to get some solder paste (it was backordered, had to wait a month or so) (http://uk.farnell.com/jsp/search...)

So I tried the 'skillet' technic I've seen in several places on the intraweb. I applied a mini-drop of the thing, put it on the skillet, and tried to roughtly follow the recommended thermal profile...

And it reflows, but badly... I have to wait until the board is about 270C (about 30C+ more than the specs) and the result is 'grainy'.

Any suggestion ? If I get that to work there won't be any limits to the parts I can start using.. mwahaha :D

Author of simavr - Follow me on twitter : @buserror

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buserror wrote:
... I've seen in several places on the intraweb.
If it's truly on your intraweb, perhaps you should talk to the folks on your local area network that authored the information. In general, though, while I'm intrigued by the skillet method (as documented on SparkFun's internet web site), I've not yet tried it.

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Maybe you should try the toaster oven method. I'm interested in trying it myself.

http://www.seattlerobotics.org/e...

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By the way, well-done photograph!

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kevinrosenberg wrote:
By the way, well-done photograph!

Thanks; well I'm a photographer, that helps :D 135mm lens mounted on bellows with an extra tube, mirror lockup, f22 and the light is from the desklamp :D

For the reflow, I'm using similar stuff as sparkfun etc... There must be something I'm doing wrong, or maybe my british solder paste is not as good as the Colorado solder paste :/

I'm using an infrared thermometer for the measure... i tried to get a 'steady' first ramp up to about 150; held it there a minute, ramped it up until it reflowed then stoped it so it cooled down...

My suspicion is that my 'lead free' paste is lame, and I need the full fat version...

Author of simavr - Follow me on twitter : @buserror

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Very cool, buserror, I like photography as well, including macros. I have a 135mm as well, the Nikon 135/2DC lens. I posted some photos at a website I wrote at http://kevin.hypershots.com . Here's one macro photo I took:

If you have a link to some of your photographs, pass it along. I alway like to look at photographs.

PS: Sorry I don't have any skillet insight to pass along. I use leaded solder on .25" pitch parts. But, I'd like to try some reflow soldering in the future for some production assemblies.

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Well I do have a bunch of stuff there : http://www.flickr.com/photos/buze/
I'm more into landscapy things and black and white; somehow, I'm not a macro head :D

I think I found 'the' reason my reflow didn't work properly.. I was reading the wrong solder paste datasheet, and thus the wrong thermal curve. That ROHS paste needs at least 250C to reflow properly, and a rather longer curve to reach it. Doh.

Author of simavr - Follow me on twitter : @buserror

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Thanks for the photo link. I'll be doing some landscape stuff in Alaska in the next few weeks. I enjoyed the curves with uprights and the shadows in your post. B&W reminds me of my darkroom days -- it can be a extemely effective medium.

Glad to hear you have an idea to improve your reflow. Please do post if you find a improvement to your last attempt.

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Ok, it seems the thermal profile needs to be bit tighter. My problem seems to be the cooling down that is too slow. I just left the board to cool where it was, it appears I need to move it off the plate...

I found an interesting description of the various phases, why there are there, and what problem can they cause here : SMT - Lead-free Reflow Profile Development

Oh, another lesson learned : don't use aluminum foil under the board, otherwise the nice snazy infrared thermometer reads... the ambient temperature !! :D

Author of simavr - Follow me on twitter : @buserror

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The finish of lead free solder looks like a dry joint in many cases. I've tried a few techniques over the years but keep on coming back to hand soldering. The trick I've found is to use flux gel. One recent technique I tried was using a butane solder torch with a hot air nozzle - it works but you gets lots of tombstoning if you're not careful. FYI 'tombstoning' is where the smt device stand on their end - it looks like a tombstone.

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Are you using RoHS, or non-RoHS paste? I've read that trying to do skillet reflow with RoHS paste is almost a lost cause, because RoHS paste doesn't have enough surface tension to pull components into position the way normal paste does, and it has a MUCH higher melting point with smaller margin of error.

That said, I reflowed about 40 boards via skillet last December using normal low-melting-point lead-enriched paste... with roughly a 20% success rate. I ended up doing the rest by hand with a hot air rework tool and got my success rate up to about 40% (60%, if you count the ones I was able to fix, as opposed to the ones that worked on the first try).

There's no place like ~/

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So what was failing ?

It is RoHS paste; I would have picked the non RoHS one if I could find it easily..!
I showed the joint to a hardware guy, and as Kartman said, he thinks they are perfectly OK.

Not wanting to put oil on the RoHS fire, but I think that if it looks fugly like that, it's lame :D And if it needs considerably more energy to make one joint, it's not saving the environment either. But heck !

Author of simavr - Follow me on twitter : @buserror

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I think my biggest problem was due to using too much solder paste. I really should have paid Pololu to make a stencil (and will, in fact, do it this fall before I make another stab at building more).

There's no place like ~/

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Just to followup on that thread, I sent this image to the manufacturer in france, and he confirmed it was a perfectly good result for the product!

It didn't stop me ordering a seringe of nicely toxic leaded paste for my next tries :D

Author of simavr - Follow me on twitter : @buserror

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One method i've been meaning to try is to set the skilet/frypan/whatever to about 100 to pre-heat the board then use the hot air re-work station to "push it over the edge"

I'm working up my courage to try it with some WTS701's i have here TSSOP56 package!

Darren

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Those whom the gods wish to destroy
they must first teach to use c
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BTW since that thread, I dumped the RoHS paste, and got perfectly toxic one instead. What a pleasure to use ! Surface tension is fantastic, the joints are lovely and shinny, and it's quickly done too, needing only about 180C to 'pop'.

In other words, if you are new to this, skip the RoHS and go direct for the leaded one...

Author of simavr - Follow me on twitter : @buserror

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Quote:
In other words, if you are new to this, skip the RoHS and go direct for the leaded one...

But then don't chew on the board.

There are pointy haired bald people.
Time flies when you have a bad prescaler selected.