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soldering SMD new idea??

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MrDEB

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I read with great interest about soldering SMD using a fry pan with a plate of aluminum under the pc board to distribute the heat.
BUT they talk about using paste flux with balls of solder within the paste. needs refrigeration and overnight deliverly.
My thought was to glue the componets using a dab of glue (Arlienes craft glue) then laying alayer of rosin flux on pins etc.
THEN using thin solder , smash the solder flat(more contact for heat absorption?) then cut lengths to go across the pins of say a SSOP-18.
heat in fry pan until solder melts. remove from heat and cool.
I am going to try this out but using a dip-18 (I have a fried PIC-got Vcc reversed)
curious if anyone has tried this??
 

3v0

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dknguyen

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In my opinion, your method of using reflowing without using solder paste defeats the purpose of reflow which is less assembly work per board after the initial setup is complete. WIth your method, you still have all the disadvantages of using a soldering iron (doing individual work on every IC, except now (you also have to work with glue) as well as all the disadvantages of reflow (you have to go search and correct all defects like bridging with a soldering iron). So for all the extra time and effort and the mess you make in order to be able to reflow the board, you still have to do all the same work as just using a soldering iron.

SMD requires VERY little solder and with your method I think you are very prone to using too much solder resulting in bridges all of which you are going to have to hunt down and correct with a soldering iron. Also, I can sort of see the solder wire rolling off the pins especially while you are setting up other ICs on the board. Why not just use a soldering iron to begin with?

I just do SMDs with a normal soldering iron and solder wire. One main reason is because I don't hate solder paste and don't like to get stencils made, or to work with them. It's also easier to hunt down all bridges and defects as you are going along then to try and find them once the entire board is done. I am not doing large runs so the initial expense and work outweight the advantages of reflow.

No, you don't need to solder SMD pin-by-pin (except when correcting bridges, though you could do pin-by-pin all the time if you really wanted to). You drag the molten ball of solder at the end of the wire across rows of pins. Similar to the method you describe except instead of laying down a piece of solder wire, I am laying down a piece of molten solder. Instead of glue (though you could do that if you wanted to) you just do a quick spot solder the two pins on opposite corners of the IC to hold it in place while you work on the IC. Heck glue or spot soldering- just hold the IC still with tweezers until the first row of pins is soldered down.
http://www.howardelectronics.com/jbc/dragsoldering.wmv
 
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MrDEB

Well-Known Member
stencils etc??

I saw a reference to stenciles in another post what and how??
in the video they sure make it look easy
what are they using (clear jell on pins??)
going to have to look at this SMD some more
 

dknguyen

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Most Helpful Member
THat clear gel is flux. I think it's not amber coloured because it is water-soluable flux or no-clean flux since it. THe drag soldering is as easy as it looks. The trick is:
-to use lots of flux
-to not use too much solder on the iron (or else it will bridge). Too little is better than too much since you can always come back with a new bead of molten solder to continue.
-you don't physically touch the pins with your iron (or else the IC moves around and the pins get flexed or stressed). YOu just let the bead of solder glide on the pins.

Also, the tip does not have to be super fine like for pin-by-pin soldering. In fact it should almost be able to contact two pins at once since it is the solder bead that does the solder distribution, not the iron itself. THe one in the video is a special tip made for drag soldering. It looks like an regular tip except it has a small hole or indent to help hold solder so the solder is carried in this solder reservoir rather than as a bead on the tip. You don't need it though.
 
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MrDEB

Well-Known Member
you don't touch the pins??

that goes against the principal or method of soldering that I learned.
heat the board and componet then add solder.
this method works I assume with no cold solder joints?
 

dknguyen

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Most Helpful Member
Yeah, I first asked about that too. Drag soldering for SMD is almost like wave soldering for through-hole, but more localized. It is the solder bath (or solder bead) alone that heats up the pins. The heating element is large enough to keep the molten solder sufficiently hot, and the molten solder has a much larger thermal mass than the pin, and is liquid so it completely surrounds the pin maximizing heat transfer. Yes, the solder will become a bit cooler as heat is transferred to the pin, but the thermal mass of the solder is large and the thermal mass of the pin is small, so the solder cools a little bit but the pin heats up a lot (like charging a smaller capacitor from a larger capacitor, small voltage drop in the large one but large voltage rise in the small one). The result is that the pin can reach sufficient temperature without direct contact from the iron.

The volume of an SMD pin is also smaller than a through-hole pin which means more surface area to volume so heat applied to the surface of the pin can reach all of the bulk inside the pin more efficiently too.
 
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3v0

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I agree with Dknguyen here. If you are only making one board you can easily solder it with an iron. Both the drag method and the removeing extra solder with solder wick work. After a while you will be soldering chip resistors faster then through hole parts.

At times I use through hole pin headers as SMD.


This board converts .05 in to .1 in for an LCD display.
 

dknguyen

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Oh yeah, 3v0 reminded me. There's also a method where you just freakin' smear the solder over the pins- you don't care if there is a bridge or not. THen you go over the pins with solder wick to suck up all the excess solder removing all bridges just leaving a thing layer which holds the IC to the board.

I don't use this method...wastes solder, wick, and flux and is messier than dragging.
 
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Hero999

Banned
Some SMT components can even be soldered on veroboard: 805 resistors and capacitors and some transistor and voltage regulators packages are suitable for this. SO8 and SO16 aren't but they're pretty easy to solder dead bug style.
 

3v0

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Mr RB

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Here's my technique for easy hand soldering of SO16 chips etc.

I use a fine tipped temp controlled soldering iron, just a standard one, I run about 325'C.

1. Drop chip on dry pcb.
2. Push chip in place using fingers,
3. Hold chip down (in place) with fingertip/fingernail of left hand
4. soldering iron dab some fresh solder on the tip
5. touch iron tip right across 3 pins of the SOIC
6. check chip is placed right
7. (repeat); dab solder on tip, dab tip on 3 pins.

3 pins at a time is about right to soak the excess solder from the tip of the iron onto the pins, and not bridge out too often. I get bridges about 1/3 of the time, and dont use wick I just wipe the excess solder off the iron tip, then touch it back on the bridge, it sucks the excess from the pins and removes the bridge.

It's very quick, it probably takes as long to push the chip in position and check it's lined up as it does to actually solder it.

The trick is to "dab" the correct amount of solder onto the iron tip each time, but this gets easy with some practice. I just use 1mm rosin cored solder in a dispenser that holds the solder end upwards so I can "dab" the tip down onto the solder end.

Bright lighting and even a magnifier are essential.

3V0, you can rejuvenate old solder paste just by heating to 60'C for a few hours. Leaving on hot concrete in the sun works, I actually use an incubator but it definitely works. The solder returns to solution within the flux paste, which itself is inert. I used the same solder paste syringe for years.
 
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DirtyLude

Well-Known Member
There's a sticker on it with some numbers; the expiry date is probably encoded somehow that I can't understand. To me, the expiry date is when it doesn't work anymore.

I'm sure there's all sorts of stuff you can worry about the details on it, but it's cheap and it works and I'm not using it any customer products so that's all I care about. The only thing that I find a pain are QFN's. I just spread a touch on the pads, place the QFN and give it some hot air from the rework station and it sits nicely.

Oh yeah, I found the manufacturer website to try and get more details, but it doesn't give anything more either. I was pleasantly surprised there was even a manufacturer website.
http://www.elodestar.com/showproduct_en.aspx?id=241
 
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3v0

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Given the price and no shipping charges I would be willing to give it a try.

I think part of the expiration thing has to do with how well it works with a stencil. That is not as much an issue with with us as in production.

What I mean by "works with a stencil" is that it gets stiffer as it ages because it looses some of the volital (sp?) compounds. Like paint that dries up.
 

dknguyen

Well-Known Member
Most Helpful Member
SMT is EASY! - once you know how to do it.
That can be said how many things? Long division, calculus, playing the any musical instrument, picking up girls...:D

More importantly SMT with an iron has a really shallow learning curve. :rolleyes:
 
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MrDEB

Well-Known Member
Thanks all

those videos are very enlightening.
Now just need right tip and no-clean flux
 

MrDEB

Well-Known Member
EGADS my board is green??

been a week since I did any work on my board using through hole.
using amber colored flux paste.
my board ( the copper) has turned green?
I probally should have applied the liquid tin before doing any soldering??
any thoughts??
 
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