I've heard of a method (haven't tried it yet) or doing SMT with hot air using an inexpensive embossing tool, and a beverage warmer. The embossing tool can be had for $25-30 from a local craft store (A.C. Moore, Micheal's or the like, or ebay???) Here's a link to the site explaining the process.
As many different directions that this thread was gone... you can see everyone has a different way of doing it. Some may be easier than others, and some better suited for different purposes.
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Brian Meade
"They who dream by day are cognizant of many things which escape those who dream only by night" - Edgar Poe
Dont follow his directions on the application of paste, he places way too much on the pads. Hand application is ok for a prototype (just use about 1/8th the amount he uses), but invest the money on a stencil if doing even small production runs.
believe it or not but SMT components are often wave soldered! especially when boards are used with SMT components on both sides.
First the "top side" SMT components are soldered to the board in the "normal" way, with solder paste applied through a solder paste mask, and then reflow soldered in an oven.
After that the board is turned downside up, and a robotic system, similar to that which places the SMT components on top of the solder paste pads, disposes little droplets of glue in-between the two pads of a SMT component (such as a resistor of capacitor), or in the middle of a larger component (IC, transistor). Then The SMT components are placed on top of the glue droplets. After the glue has hardened the board can be turned over without the glued components falling off, now the glued SMT components can be wave soldered, the solder of the already soldered SMT components on the top side might re-melt, but that is normally not a problem.
Some precautions must be taken while designing a PCB with wave soldered SMT, for example so that small components do not lie in the "shadow" of nearby large ones that prevent the wave to reach them. Also some of the copper pads that are last to be soldered are often made somewhat larger, so they can take excess solder without problems. Integrated circuits are often rotated diagonally (45 degrees), so the solder flows better over their pins.
Parts_man73,
I personally once did some SMT soldering with a modified hot air paint burner, it works, but you need to make sure the airflow is reduced, or you will blow off all the components from the board, also you need to set the paint burner as low in temperature as possible, you want to solder the board, not reduce it to ashes.
One way to solve both problems is to put a filament lamp with a similar wattage to the paint burner in series with it, so the paint burner gets only halve the wattage.
by the way,
The easiest way to solder SMT IC's (Flat pack etc), in my opinion, is to use a soldering iron with a tip that has a "hollow" in the end (specially made for the purpose), the hollow is filled with a tiny droplet of molten solder, and that droplet is drawn across the pins of an integrated circuit.
Very important is to clean the tip of the soldering iron regularly on a wet sponge. And to keep some solder-wick at hand to remove excess solder, and a syringe with solder flux is also often invaluable.
Not that I totally recommend this method, but for most SMT desoldering, I use a heat gun connected to an autotransformer (adjustable AC power supply)... that allows me to control the heat pretty well (sorta like the light bulb in series except more adjustable). And depending on the board, I also have a hotplate (like you'd use on a buffet table) which I use for preheating the board. I have used the hotplate to solder and desolder, but it tends to burn the PCB a little bit if you get it hot enough to melt the solder on the other side.
Once the board is preheated, I take the heat gun and melt the solder, and then use a handi-vac (suction pickerupper tool) to pull the chip. Of course soldering is easier... just do the opposite, except placing the chip before the solder is melted. Or I use a very fine tipped soldering iron, or the drag soldering method with a lot of flux.
Just another option, depending what hardware you already have on hand... if you don't already have some of this stuff, it may be cheaper to just buy a hot air tool. The heat gun is nice though since it's able to heat most chips all at the same time. Just make sure you practice on junk boards before trying it on something important [noparse]:)[/noparse] .
Pat, thanks for the reply. I like your approach. I was a bit weary of the hot-plate/fry pan only approach and the hot air only approach but using them together compliments the pros and minimizes the cons.
The only electronics tools I have in my home workshop are a natty old fire starter radio-shack soldering iron I got when I was 12, and a couple of old multi-meters purchased around the same time I have the basics in my shop at work and do thru-hole work there, but I'm putting together a shop at home so everything will be new (or new used).
In the picture you can see that a SMT IC is first soldered with one of it's corner pins to the board. This is done so it can't move anymore. One main problem with soldering SMT components is that they are so light that the smallest movement sends the component flying. By first soldering the IC to the board with one pin, the IC is fixated. Next the three other corner pins are done, to make sure the IC is mounted flat on the PCB, and also to make sure it wont com loose when you melt the solder on one side of the IC again.
The big trick shown here is the use of "solder wick" (thin braided copper wires dipped in flux).
Normally solder wick is used for de-soldering, by sucking the solder from a solder joint into the wick.
But in this application the solder wick is flooded with solder, so it is used to transfer the heath to all the pins on one side of the IC, and also to "wet" all the pins with solder because the solder naturally flows by capillary force through the wick.
An excess of solder over the whole side of the IC, can be removed by moving the wick a bit to a "clean" part of the wick.
Then the other side is done, and the IC is soldered.
Has anyone got any new developments? Sorry to be gone for a while. I left my machining job to go back to computer building. I need to find another job soon. I am begining to dislike where I am working. I like building computers but my employer is not providing me with the necessary tools. Sorry to complain.
Later.
Not sure what you mean by new developments, I did find out that we use the temperature profile provided by the manufacturer of solder paste we use when reflowing boards. This is the most critical component of the profile on all boards we make.
I have a quick question about soldering I want to put the compass on my protoboard and i am wondering how I can solder it then connect it to thr prop once you solder something to the board how do you connect something to one of it's pins?
I have not done anything myself. I plan to buy a dev. kit for learning how to program a cpld device. Does Parallax have any plans to get into the CPLD or FPGA chips?
Later.
Comments
www.zianet.com/erg/SMT_Soldering.html
As many different directions that this thread was gone... you can see everyone has a different way of doing it. Some may be easier than others, and some better suited for different purposes.
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Brian Meade
"They who dream by day are cognizant of many things which escape those who dream only by night" - Edgar Poe
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Paul Baker
Propeller Applications Engineer
Parallax, Inc.
Post Edited (Paul Baker (Parallax)) : 2/26/2007 9:05:26 PM GMT
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Brian Meade
"They who dream by day are cognizant of many things which escape those who dream only by night" - Edgar Poe
believe it or not but SMT components are often wave soldered! especially when boards are used with SMT components on both sides.
First the "top side" SMT components are soldered to the board in the "normal" way, with solder paste applied through a solder paste mask, and then reflow soldered in an oven.
After that the board is turned downside up, and a robotic system, similar to that which places the SMT components on top of the solder paste pads, disposes little droplets of glue in-between the two pads of a SMT component (such as a resistor of capacitor), or in the middle of a larger component (IC, transistor). Then The SMT components are placed on top of the glue droplets. After the glue has hardened the board can be turned over without the glued components falling off, now the glued SMT components can be wave soldered, the solder of the already soldered SMT components on the top side might re-melt, but that is normally not a problem.
Some precautions must be taken while designing a PCB with wave soldered SMT, for example so that small components do not lie in the "shadow" of nearby large ones that prevent the wave to reach them. Also some of the copper pads that are last to be soldered are often made somewhat larger, so they can take excess solder without problems. Integrated circuits are often rotated diagonally (45 degrees), so the solder flows better over their pins.
Parts_man73,
I personally once did some SMT soldering with a modified hot air paint burner, it works, but you need to make sure the airflow is reduced, or you will blow off all the components from the board, also you need to set the paint burner as low in temperature as possible, you want to solder the board, not reduce it to ashes.
One way to solve both problems is to put a filament lamp with a similar wattage to the paint burner in series with it, so the paint burner gets only halve the wattage.
by the way,
The easiest way to solder SMT IC's (Flat pack etc), in my opinion, is to use a soldering iron with a tip that has a "hollow" in the end (specially made for the purpose), the hollow is filled with a tiny droplet of molten solder, and that droplet is drawn across the pins of an integrated circuit.
Very important is to clean the tip of the soldering iron regularly on a wet sponge. And to keep some solder-wick at hand to remove excess solder, and a syringe with solder flux is also often invaluable.
Mahjongg
Once the board is preheated, I take the heat gun and melt the solder, and then use a handi-vac (suction pickerupper tool) to pull the chip. Of course soldering is easier... just do the opposite, except placing the chip before the solder is melted. Or I use a very fine tipped soldering iron, or the drag soldering method with a lot of flux.
Just another option, depending what hardware you already have on hand... if you don't already have some of this stuff, it may be cheaper to just buy a hot air tool. The heat gun is nice though since it's able to heat most chips all at the same time. Just make sure you practice on junk boards before trying it on something important [noparse]:)[/noparse] .
Pat
The only electronics tools I have in my home workshop are a natty old fire starter radio-shack soldering iron I got when I was 12, and a couple of old multi-meters purchased around the same time
-R
Not sure exactly how they are doing it, or how it turns out, anyone care to guess as to what we are seeing there?
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Brian Meade
"They who dream by day are cognizant of many things which escape those who dream only by night" - Edgar Poe
The big trick shown here is the use of "solder wick" (thin braided copper wires dipped in flux).
Normally solder wick is used for de-soldering, by sucking the solder from a solder joint into the wick.
But in this application the solder wick is flooded with solder, so it is used to transfer the heath to all the pins on one side of the IC, and also to "wet" all the pins with solder because the solder naturally flows by capillary force through the wick.
An excess of solder over the whole side of the IC, can be removed by moving the wick a bit to a "clean" part of the wick.
Then the other side is done, and the IC is soldered.
Martin (Mahjongg).
Later.
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Paul Baker
Propeller Applications Engineer
Parallax, Inc.
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Paul Baker
Propeller Applications Engineer
Parallax, Inc.
Later.
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Paul Baker
Propeller Applications Engineer
Parallax, Inc.