Best soldering iron for smd



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Re: Best soldering iron for smd

Postby eatyourguitar » Mon Nov 20, 2017 9:12 pm

https://www.amazon.com/MG-Chemicals-Lea ... B071D7SM1C

https://www.aliexpress.com/store/produc ... 08836.html

https://www.ebay.com/itm/Barnstead-Ther ... 2363416148

you can then thin down your paste as needed by adding IPA or liquid flux. if I had a jar of paste I would just keep it sealed in the fridge and take some out for small jobs. I don't make a big syringe and leave it out. the paste can dry and become %100 waste. some things are impossible with the iron. hot plate is cheaper than the irons that I would like to use for SMD.
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Re: Best soldering iron for smd

Postby Confuzzled » Tue Nov 21, 2017 10:21 am

culturejam wrote:I had a big detailed post but the forum ate it. :grumpy:

The key for me is getting the finest tip possible. I have a separate tip for SMD that I swap out. It's this one: http://amzn.to/2xHlDP2 It fits a few of the hobby-grade Hakko irons (they are relatively reasonably priced). These tips last a loooooong time. The most popular hobby Hakko is the FX-888.

Second thing is to get fine solder. I use 0.031 for standard through-hole stuff, but 0.020 for SMD. Flux is critical, which means either get the good solder (Kester, etc) or consider getting some flux paste in a syringe.

My process for passives and transistors: Apply a very small amount of solder to one pad. Use tweezers to position the part and then put down-pressure on the part as you reheat the soldered pad. The part will "suck down" onto the pad. Then you can solder the other pad(s). Sounds complicated, but it's not so bad.

Also, if your eyes aren't eagle-sharp, you might consider a magnifier of some sort.


What is SMD?
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Re: Best soldering iron for smd

Postby eatyourguitar » Tue Nov 21, 2017 4:26 pm

SMD = Surface Mounted Device
SMT = Surface Mounted Technology

you hear them used interchangeably to refer to a PCB or build style that has little or no through hole parts.

if someone says "SMD resistor" that would be more correct than for example "SMT resistor" since a resistor is a device not a technology. people talking 1206, 0805 etc.. these are the sizes of the packages for a two terminal device. the IC are usually SOIC or TSSOP for opamps and SOT-23 for any 3 terminal device.
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Re: Best soldering iron for smd

Postby BetterOffShred » Tue Nov 21, 2017 5:02 pm

They are tiny components that don't go through a hole. They lay on top of the board and are soldered to the surface.
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Re: Best soldering iron for smd

Postby spruce_moose » Fri Nov 24, 2017 8:05 am

I use a $20 digital iron from Ali for home and a Weller at work. Both do the job exact same job, except the cheapie doesn't have a timer shutdown. The 240V cable to the $20 iron is a tad too rigid as well. Might replace it at some point.

I am personally digging the 900M-T-LB tip. Can get into tight spots but still sustains enough heat to do most through-hole.
From what I've found, you can solder pretty most things with a variety of tips, but couldn't work without the following:

-good lighting
-no-clean flux pen
-solder wick
-good tweezers
-eye loup

With those things you could probably still use a soldering iron with a tip the size of a butter knife and get a way with it.

The general process I use is to tack a few legs in place, add an excess amount of solder to each side of legs on an IC, then flux it and drag the solder along. Take off the excess with wick, do the whole board - then clean with iso and visually check. It's much easier to see the quality of a join when flux isn't doing weird stuff to the light. If the soldering looks messy/dull/gluggy it's easy to dab the flux pen around and redistribute the solder by continuously cleaning the tip and then dragging it between 2 or more points.

I'd really recommend getting a cheapo electric hot-air station - https://www.aliexpress.com/item/Domesti ... 33841.html .

Everything from MSSOPs, resistors and caps to 0.4mm pitch QFN/DFNs will reliably solder just by tinning the pads and dropping the chip on. Solder

paste is handy though if you have it! The trick is to keep the chip on the fringe of the hot air while heating the pads before you drop it on so you don't get cold/bad joints.. a few taps with the tweezers and then let the surface tension align things. Just a bit of practice to get the timing right :) cook it too long and the flux will dry up.. wick it, back to square one.

The heat plate linked by eatyourguitar could possibly be handy in combination with hot air. For e.g. tin/flux-pen all the pads, use the plate to keep the board at 120degrees or so, and then use the hot air with one hand while you drop chips with the other. It could just be worth getting a stencil and hand pasting, then using the hot plate to solder everything. Holla if you need any tips there. I've got a few shortcuts in that area that make life a bit easier.
Last edited by spruce_moose on Sat Nov 25, 2017 3:09 am, edited 1 time in total.
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Re: Best soldering iron for smd

Postby eatyourguitar » Fri Nov 24, 2017 12:55 pm

I never thought about using the hot plate as a pre heater but actually that would probably work. most pre heaters are shooting air up from the bottom with the PCB flying in a jig. My suggestion was to skip the expense of a stencil and to apply solder paste to the pads in uniform amounts with the solder paste gun. some diy PCB's that you can buy do not have a stencil period. it is different when you own the company, when you want to make 100 units of something. you can order the stencil from the same factory where you order the pcb. here is an open source jig for people ordering custom stencils that fit this jig.

http://www.hoektronics.com/2012/10/27/s ... -stencil8/

you buy the pegs from any metal peg supplier like mcmaster.com

you order the peg board from a machine shop

https://www.emachineshop.com/

if you want to look at a real pre-heater check this. in order from $40 to $10,000

https://www.aliexpress.com/item/110V-BE ... 91211.html
https://www.amazon.com/NEWTRY-50℃-350℃-Preheater-Station-Preheating/dp/B06XD4Z4QG/
https://www.amazon.com/Popsport-Preheat ... 0728HYF72/
http://www.zeph.com/airbathseries.htm
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Re: Best soldering iron for smd

Postby imJonWain » Fri Nov 24, 2017 3:49 pm

^at my work we do what he describe and rarely use stencils even for our own boards (<20 usually). I use a small solder paste gun to put paste on pads, place the components and then heat the board. We use an oven but it's the same idea and works well after some trial runs.
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Re: Best soldering iron for smd

Postby spruce_moose » Sat Nov 25, 2017 3:28 am

There's very reasonable stencils via Elecrow, and I've found you can get around the stencil machine by using a thin rubber mat on a benchtop. Aligning manually isn't too much of a pain for small batches (unless it's white mask and HASL! hard to see!) The rubber grips the board with some downward pressure and when the frame is weighted it grips to the rubber too. Gets a surprisingly good gasket for the fine pitch stuff.

eatyourguitar wrote:My suggestion was to skip the expense of a stencil and to apply solder paste to the pads in uniform amounts with the solder paste gun.


I've seen a paste-application machine project somewhere that looks like a modified 3d printer. Wasn't high resolution, but with a finer syringe tip and that would be excellent to get around stencils for small batches! Maybe even possible to use a ULP in a DIY Eagle project to get the required g-code data.. if only I could code :facepalm:
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Re: Best soldering iron for smd

Postby multi_s » Sat Nov 25, 2017 4:48 am

@tha spruce, you can try just export the pad layer as DXF or something from eagle to a CAM program and "mill" the pads as pockets etc. but instead of milling you are dumping paste. you don't have to code anything.


most places will make stencils really cheaply now and some american board houses even include a free kapton stencil with an order. if you have access to even a weak laser you can also cut your own kapton or plastic single to few use stencils. there is also really interesing approach for single use where a guy laser cuts a sticker sheet, and puts the cut sticker on teh pcb then applies paste with a squeegee. pretty neat but i have never tried it since even metal cut stencils run as low as 20-40 USD.

it depends on the complexity of the board i guess but really stencils are FAST. and even if the board is simple, you can make arrays of boards with a matching stencil and paste 10s at a time.
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Re: Best soldering iron for smd

Postby eatyourguitar » Sat Nov 25, 2017 11:29 am

I can make stencils in eagle using eagle without using ULP. you need to make a new outline around the PCB for the stencil and you need to add registration marks that correspond to fiducial marks on the PCB. when I send gerbers I never send *.GTP *.GBP since P is for "Paste" or "Pad". when you are in the cam job this is called "pad mask top" and "pad mask bottom". when you are in the .BRD this is called Tcream and Bcream. I have never had a need to do this myself but I know I can make gerbers with this technique. gerbers are universal you can use them for any material. you could in theory use the same process to send a file to a CNC paste dispensing bot. if you need G code you can get the ULP here

https://www.element14.com/community/doc ... f-all-time
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