OT: Reflow, MLF, Solder Paste and a home made oven

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#1
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Hello,

This is my first time soldering with the homemade oven :) Anyway I'm about to apply the paste to the pads and have a semi important question for the home oven experts.

Do I apply the paste to each pad individually? OR can I put a continuous bead across all pads?

I did a little experiment with an old 44 TQFP and the continuous bead worked well...there were no shorts and the solder flowed to the pins ok...

BUT

The packages I want to REFLOW now are MLF.

Ideas?

Thanks,
OC.

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I use a continuous bead. The solder surface tension pulls it to the copper. I've done MLF28. Search this site for toaster to get more info.

Smiley

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Thanks Smiley,

I've been reading the other posts on the site about using the toaster oven, I just couldn't find if people were putting the paste just on the pads or used a continuous bead.

I too am going to put down MLF28 package...the CP2101 :) I've hand soldered it in the past but it was a major pain.

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Surface tension is a great invention..thank God.

Soldermask too is another fine invention.
Unfortunately soldermask can sometimes get to be a bit soft and plasticy. Solder then tends to stick to the soldermask . so beware if you are getting weird behavour from your home reflown batch oven you might have a fine webbing of solder across the board..

Dont forget to try to match thermal profile of the toaster to that specified by component manufacturer especially if you have any ceramic compnents in the assembly.

AVX have some finepapers on this.

Good luck with your experiment.

PS.. if you have a bottle of N2 and can brin the O2 content below 0.5%you will have amazing results..\

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Smiley,

What did you use to apply the paste to your PCB? I am not having much sucess with this process....actually its driving me nuts. I put a continuous bead for one part and it created a nice long short..hehe. I think I put to much paste. Some pads on the part are not used so I guess the solder had no where to flow (Bare PCB with NO solder mask). I guess I'll keep trying....

SIDE NOTE:

Never stop watching what you are doing to try and explain what you are doing with toaster oven to wife. This will result in a very over cooked PCB and PCB components. Digikey oh Digikey you thou art my friend!

Oc.

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You will be suprised how LITTLE paste you need.

But to be honest I would not bother with this home brew stuff as when the industry goes lead free in 18months time the temperature to melt the solder to get it to flow and the melt down point of the silicon are getting very close. Also the tension pulling a device into alignment which is so usfull with the present lead loaded solder all but disapears with the none leaded stuff.

Keep it simple it will not bite as hard

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I have been making a gradule move from "Through Hole" to SMT over the pase few months. Atmel is motivating my switch because of the uCs that I hace been using are SMT. I have been hand soldering everything SMT and, its really rough on the already nearly blind eyes. I'd like to try the convection oven approach. Is there a particular oven that works better then some other? Do the consumer style ovens provide good enough temperature control or, would I need to provide my own temperature control? And, how in the heck, even with solder paste, do you get everything in place without knocking everything off grid that has already been placed? I am wondering if I have the manual dexterity to accomplish that.

You can avoid reality, for a while.  But you can't avoid the consequences of reality! - C.W. Livingston

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Well, this could be found by searching the forum for toaster, but...

I use a syringe of solderpaste made by AMTECH and bought from howardelectronics.com for $16.00 (doesn't need refrigerating). I make a band that is about 1/3 the width of the pads across the pads. I guess it is about 1 mm in diameter? I also use a 500 degree F thermocoupe that comes with a multimeter from Sears ($30). I hand time the process to match the reflow specs for the solderpaste, but I find that I can watch it to see when the organics boil off and the solder reflows and gets pulled to the pads to determine when the soldering is done and I then ramp down the heat. I used the cheapest toaster oven I could find.

Also, the comment that one shouldn't bother because the industry is going lead free in 18 months is off target for us prototypers. I'd bet my career that I can get lead based solder paste in 10 years to do prototyping work.

Smiley

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Thanks Smiley,

I have a syringe type solder paste as well though the hole on the needle is a bit large. (Solder paste type: Kester R276). It only cost $16 CND from a local electronics shop.

I too am using a DMM and thermocouple to follow the reflow heat profile. After a few tries last night I was able to solder my boards.

Microcarl: The solder paste holds the components to the PCB rather well, so I don't think you'll have a problem with putting parts down. Just don't drink 10 cups of coffee before you start placing components :)

As for my "oven". I got it at a surplus store for $20 bucks and it works great. You might want to check out [url] http://www.circuitcellar.com/ren... [/url] . The Grand prize winner's project was a home made reflow oven.

Oc.

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Hey,

For my SMD solder paste I push the paste out onto a scrap, then use a needle to put the paste on the pads. So you can imagine how little paste you need!

Also Oc - where'd you pick up that solder paste? I had to order from Digikey which is about $40 CDN...

Regards,

-Colin

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www.howardelectronics.com $16 AMTECH syringe doesn't need refrigerating.

Smiley

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Thanks guys for the tips and vote of confidance. I will start looking for a toaster oven.

Oh, and Ocnek, the coffee thing would be a very hard thing!

I'll need a week or two to bribe the wife, er, I mean convincer her that I really need one. I'll re-visit this topic at a later date.

You can avoid reality, for a while.  But you can't avoid the consequences of reality! - C.W. Livingston

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Does the toaster oven method work on fairly fine lead pitches? I've been
hand soldering some prototypes and the TQFPs, PQFPs, uMAXs, etc aren't
so bad, but one board has a 40 pin *0.5mm* pitch FPC connector that reduces
me to a quivering blob of jelly by the time I get it mounted (without shorts).
I would love to try this if the odds of ruining $30 4-layer boards were less than
with me doing it with an iron. I also wonder how a hot-air iron might work on these
connectors. Anyone using them?

Thanks,
Tom Pappano

Tom Pappano
Tulsa, Oklahoma

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Colin: I got the solder paste at B&E electronics [url]http://www.be-electronics.ca/ind... [/url] Kester R276SR No-Clean Paste Syringe 35grams $16.38 + GST

Oc.

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Has anyone used a heatgun to solder a chip in place? Using solder paste and the gun at low speed so that the chip does't get blown away? ...I soldered my broken water pipe with one....but that's different I guess :-)

John Samperi

Ampertronics Pty. Ltd.

https://www.ampertronics.com.au

* Electronic Design * Custom Products * Contract Assembly

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Quote:

Has anyone used a heatgun to solder a chip in place?

Hi John, now you have told my secret! ;-)
Seriously, we have an nice Riobi heat gun that has an adjustable heat setting. We set it with an external temp probe and, as long as you don't linger in one spot too long, it does a great job.
Just leave the connectors off & do them later by hand - Molten Molex is not pretty ;-)
Cheers
Ivan
realtimedesigns

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Quote:
we have an nice Riobi heat gun that has an adjustable heat setting.

I have a Black and Decker, 2050W 600degrees celsius, with a water pipe soldering setting :-) and an Arlec unit with only 2 settings. May have to pop in and get some expert guidance....well as soon as I can get some solder paste that does not expire before I open the tube like my last lot from Farnell.

John Samperi

Ampertronics Pty. Ltd.

https://www.ampertronics.com.au

* Electronic Design * Custom Products * Contract Assembly

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There is another option that does not require heat gun or oven.
Use very thin solder wire, to prevent too much excess, just run down the pins with solder and wire, then remove all shorts with solder wick. Just remember to solder at least one pin down to hold device in place prior to general soldering.

Keep it simple it will not bite as hard

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Hello all!

Is there a limit to how many times I can bake my PCB. I would like to build my boards in steps. i.e. Put the IC's on ->bake<- put all passives on ->bake<-

The reason I would like to follow this process is that I keep knocking some of the components off their pads if I try and populate the whole board for a single run in the oven.

Thanks,
Oc.

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sutton wrote:
There is another option that does not require heat gun or oven.
Use very thin solder wire, to prevent too much excess, just run down the pins with solder and wire, then remove all shorts with solder wick. Just remember to solder at least one pin down to hold device in place prior to general soldering.

I use 'drag soldering' with a special Metcal mini-hoof tip that holds a small amount of solder.

Leon

Leon Heller G1HSM