Hi,
I would like please an advice about a soldering paste for cms. I plan to use the kitchen electric oven. I do not need big quantity.
What brand and apply technic (needle, else?) do you use, please?
Thanks for your experience.
I would like please an advice about a soldering paste for cms. I plan to use the kitchen electric oven. I do not need big quantity.
What brand and apply technic (needle, else?) do you use, please?
Thanks for your experience.
I like Kester EP256 solder paste for use with a stencil. It's a 63/37 lead paste, but it flows easily, and behaves really well. Early on, I tried using a syringe, but it's just too time consuming and sloppy. A custom stencil is truly the way to go. I'm using a 0.12 mm thick stencil that I order with PCBs from PCBway. I get the version pre-tensioned onto an aluminum frame. I can only find this paste in 500g jars, but it keeps well in a refrigerator, much longer than the expiration date suggests.
The process: put the PCB on the bench, immobilized between some taped down corner mounts, put the stencil over the PCB, line it up, tape the four sides of the frame down to the bench, apply paste with one pass of a stainless steel squeegee. Remove three sides of the tape, lift the stencil as if it was hinged off of the fourth piece of tape, remove the PCB, and then place the parts and reflow.
I use a Hakko infrared pre-heater running a program that seems to work well via trial and error. It gets the PCB up to 180ºC as quickly as it can, which ends up taking around 3.5-4 minutes to get to 170ºC, as read from a thermocouple taped to the PCB with Kapton tape. Once it's barely starting to flow, I use a hot air wand to bring each part of the PCB up to reflow temperature. With this paste, taking too long to get to reflow causes graping and generally non-smooth and shiny joints, but getting there too fast prevents the flux from fully activating and steam/gases from baking out. There's definitely some trial and error involved and I would strongly suggest that you tape a thermocouple to the board so you can see what is happening. The Hakko has one built in that it uses to control the temperature profile, but you can use your own if you're using a random oven.
Another reason why a stencil is so great is that by designing the footprint properly, you can deposit precise amounts of solder paste, and reliably handle parts with die attach pads like DFN and QFN and SO-8 parts with DAPs. Most small area pads should get a solder paste stencil aperture equal to the pad size, but with larger pads, like die attach pads, a large aperture should be broken up into smaller apertures that only cover a percentage of the total area, perhaps around 60%. This prevents excess paste from lifting and floating the part away from the pads at the edge of the part. It sounds overly complex, but yes, there are a lot of things to get right if you want it to work 100% reliably.
Best of luck to you!
The process: put the PCB on the bench, immobilized between some taped down corner mounts, put the stencil over the PCB, line it up, tape the four sides of the frame down to the bench, apply paste with one pass of a stainless steel squeegee. Remove three sides of the tape, lift the stencil as if it was hinged off of the fourth piece of tape, remove the PCB, and then place the parts and reflow.
I use a Hakko infrared pre-heater running a program that seems to work well via trial and error. It gets the PCB up to 180ºC as quickly as it can, which ends up taking around 3.5-4 minutes to get to 170ºC, as read from a thermocouple taped to the PCB with Kapton tape. Once it's barely starting to flow, I use a hot air wand to bring each part of the PCB up to reflow temperature. With this paste, taking too long to get to reflow causes graping and generally non-smooth and shiny joints, but getting there too fast prevents the flux from fully activating and steam/gases from baking out. There's definitely some trial and error involved and I would strongly suggest that you tape a thermocouple to the board so you can see what is happening. The Hakko has one built in that it uses to control the temperature profile, but you can use your own if you're using a random oven.
Another reason why a stencil is so great is that by designing the footprint properly, you can deposit precise amounts of solder paste, and reliably handle parts with die attach pads like DFN and QFN and SO-8 parts with DAPs. Most small area pads should get a solder paste stencil aperture equal to the pad size, but with larger pads, like die attach pads, a large aperture should be broken up into smaller apertures that only cover a percentage of the total area, perhaps around 60%. This prevents excess paste from lifting and floating the part away from the pads at the edge of the part. It sounds overly complex, but yes, there are a lot of things to get right if you want it to work 100% reliably.
Best of luck to you!
Hello Monte McGuire,
Just posted elswhere cause I haven't sucess here before you post.
Thank you so much for your advices.
Just posted elswhere cause I haven't sucess here before you post.
Thank you so much for your advices.
Pardon my ignorance, but what does a "stencil", as mentioned in post # 2, look like? Slowly reading into SMD soldering territory, it is all foreign to me..
Lead solder in a kitchen oven?? No! What are you thinking?
SMD291SNL10 is what I use.
https://www.mouser.co.uk/datasheet/2/73/SMD291SNL10-746146.pdf
I'd suggest not doing any soldering in a food preparation area as a given. I adapter a cheap sandwich toaster and its for soldering use only now.
If you type "solder stencil" into a search engine and select images, guess what appears? To use stencils effectively you need some means to hold the stencil (a stencil frame) firmly while squeegeeing.
After the 3e YT clip it finally dawned on me what the stencil does. My bad..
Do you gentlemen make the stencils yourselves or order those with the PCB's?
Do you gentlemen make the stencils yourselves or order those with the PCB's?
I also do not expect the OP to have an $1800 IR reflow device. Merely describing what I use as accurately as possible. Nobody should be reflowing any PCBs in any kitchen appliance for any reason, no matter what type of paste. Might as well throw them onto a bonfire instead... 🙂
https://www.flickr.com/photos/135181977@N06/albums/72157682590706812
Ok. I wanted to follow a tutorial from ianCanada with his kitchen oven, so better a vertical toaster ? How much time and pot number would you advise with a toaster, please ?
280° ?
Ok. I wanted to follow a tutorial from ianCanada with his kitchen oven, so better a vertical toaster ? How much time and pot number would you advise with a toaster, please ?
280° ?
Here we get SMD reflow machines used for cell phone repair starting about $15...those with temperature control may be in the $40 range for a good one.
Also used for computer motherboard repairs.
This is a seller's image, copied off the net.
Size is within one foot width, maybe 8" high, 8" depth.
With temperature control, so you can see and work properly.
Better than a toaster or oven.
The branded ones from Weller and Hakko are much more expensive.
Also used for computer motherboard repairs.
This is a seller's image, copied off the net.
Size is within one foot width, maybe 8" high, 8" depth.
With temperature control, so you can see and work properly.
Better than a toaster or oven.
The branded ones from Weller and Hakko are much more expensive.
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A hot air wand alone can be difficult to use and torturous to components - they go from zero to over-temp instantly, and that violates the datasheet limits. An oven with a controller is a lot more predictable. Solder paste also specifies a temperature ramp, and the rate is usually no more than 2-3ºC per second.
Find a paste you want to use, then look up the datasheet. The manufacturer will specify a suggested thermal profile. If there's no datasheet or suggested profile, try searching for "reflow soldering profile". It's mostly dependent on the alloy used - 63/37 will be different than SAC305.
It doesn't matter what's producing the heat, the temperature vs. time curve is the important part.
Using this solder paste from ChipQuik
https://www.mouser.at/datasheet/2/73/TS391AX-1150469.pdf
It is a T4 (very important parameter, the more metal the better), Sn63/Pb37 and no clean. Very nice 👍👍👍
https://www.mouser.at/datasheet/2/73/TS391AX-1150469.pdf
It is a T4 (very important parameter, the more metal the better), Sn63/Pb37 and no clean. Very nice 👍👍👍
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I assume with clean material inside, the thin and marrow ICs autocenter themselves more easilier on the pcb pads, avoiding jonction risks between pads during the heating melting process ?
Yes, they center perfectly. Make sure you do not blow them away.
question - for a QFN 48pin plus ground slug i need to use something low temperature (not lead free). I noted 138degC solder paste (a good 70-90degC lower than leaded). I was going to get that with a low temperature tacking flux. Has anyone used a low temp solder for smt?
It will need to play well with signals ~25Mhz and it will be soldered using an iron (the ground/thermal pad is connect to both sides).
Solder paste: https://www.digikey.co.uk/en/products/detail/chip-quik-inc/SMDLTLFP10/5180410
Flux: https://www.digikey.co.uk/en/products/detail/chip-quik-inc/SMDLT-5M/14636566
It will need to play well with signals ~25Mhz and it will be soldered using an iron (the ground/thermal pad is connect to both sides).
Solder paste: https://www.digikey.co.uk/en/products/detail/chip-quik-inc/SMDLTLFP10/5180410
Flux: https://www.digikey.co.uk/en/products/detail/chip-quik-inc/SMDLT-5M/14636566
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Don't use a vertical toaster, i.e., one intended for sliced bread. The parts will fall off.
What you want is a toaster oven. I use a Black & Decker one that set me back about $40 if I recall correctly. Aim for one with top and bottom heaters, preferably over 1 kW. If you google "toaster oven reflow soldering" you'll get many good links and videos.
+1 for a solder paste stencil and 63/37 Sn/Pb solder paste. I use some by ChipQuik. It works very well. Just follow the reflow curve that comes with the solder. I use a thermocouple thermometer by Amprobe (Fluke's el-cheapo brand) for this.
Tom