Double-sided reflow at home

[Smashcat]

Hi, first post here - I have a T-962A at home I use to reflow my prototypes, and up till now have only used it for single-sided boards - manually soldering any SMA parts on the bottom if needed. Wondering if anyone's tried double sided reflow with one of these types of oven. I'm thinking of using paste with a standard temperature profile (up to around 230 degrees) on the bottom side, then loading the top, and using a low temp paste (reflow at 180 degrees) with an appropriate profile, so the parts on the bottom don't desolder. I could use glue, but it seems it could be easier to just do it this way instead?

PS: I also made custom firmware for this oven (also works on the smaller T-962), based on the Teenage Engineering version, but with updated UI more options, completely pointless Pacman screensaver etc on my Github if anyone's interested 

Thanks,
Scott

[SMdude]

I do double sided all the time. I have some spacers to hold the board up off the tray.
First reflow I have all small parts, smt resistors caps and ic's, then the second side has the larger smd such as inductors and electro caps and whatever other smaller smd's didn't fit on the first side.
I'm using GC 10 paste and haven't had any problems with parts moving or falling off on the bottom side during the second reflow. My panels take up 2/3 of the tray.

Did you include more custom reflow profiles in your firmware? That would be really handy and sometimes a longer time limit would be good too. When you have a bunch of larger smd inductors and caps close together they need just a little longer to reliably get all the solder to flow.

[Kasper]

Worked fine with my $20 (used) toaster oven with the same cheap solder paste on both sides. Was small boards with small components.

[OneGeekGuy]

I have used the same oven to solder PCBs with components in both sides without problem, other point is that this oven only have the Heating element on TOP, so even if you have really god isolation (Upgraded by yourself) the temperature below will we little lower...

Sometimes...(I don't recommend to do this) I used a small sheet of wood below the PCB to reduce the heat transfer to the low side and by this way prevent components to fall.

I always use the same solder paste in both sides...

BR

[Kean]

Same as the others here, I do double sided reflow regularly without issue and no special processes.  I use a T-962A with GC10 paste and metal standoffs to keep the PCB off the tray.

You may need to use glue if you must have heavy components on both sides, otherwise the surface tension is generally enough to keep parts in place during the second pass.

[Berni]

I do double sided boards in an reflow oven all the time.

No special solder or anything, just regular leaded solder paste, no special precautions for holding components down. Only thing i do is use small pieces of FR-4 in the corners of the board so that the PCB is not sitting directly on the metal floor of the oven.

The heat still makes it trough the board even if only the top is being heated. You would need a really fine tuned profile to not have the heat make it trough while still soldering all of the top side reliably. But it does not matter because clean solder has a very high surface tension, so even if solder joints on the bottom side reach melting temperature the components don't fall off due to surface tension still being there.

The only components that might have an issue are very large heavy components with very little solder area under them. This might be things like large inductors or connectors with few pins but a large bulky body. But if you are lucky even those will be just fine since sometimes the component is so large that it helps cool its own solder joints. But you will certainly not get things like SMD resistors or MLCC capacitors falling off the board during reflow since they are not nearly heavy enough to overpower the surface tension.

Go ahead and take a old dead board, heat it up to soldering temperature with a hot air station and carefully flip it over, nothing will fall off until you actually give the board a decent wack with a screwdriver handle to knock the components loose

[asmi]

I've done a ton of double-sided boards, and there was never a case of even single part falling off - molten solder has very high surface tension, so it will hold bottom parts in place with no problems.

[Rat_Patrol]

I also run double sided daily, zero issues.

I even use the same solder and the same reflow program. I use a Controleo converted toaster oven.

The bottom of boards *should* be limited to small components for just this reason. If you have large ICs on the bottom, you may run into issues, and may need different temp solders.

I use a spacer (small, junk PCBs) to keep the board suspended so the components don't touch the plate, and I've yet to have a failure.

[Kjelt]

I wonder what the paste manufacturers have to say about a second 200+C heating cycle ?
Any chance of "cold solder" joints or brittleness, that kind of stuff.

[Berni]

Well if anything melting it would reset its mechanical properties. At that point the solder is already in the form of a solid blob so the paste flux is not needed anymore(Since its not there anymore because it boiled off on the first cycle).

But smaller temperature cycles say 20 to 100 °C and back for months on end does make solder brittle combined with the mechanical strain of thermal expansion. This is most of the reason why laptops die.

[asmi]

This is most of the reason why laptops die.

As far as I know, by far the most popular reason for laptop death is a liquid spill.

[SMTech]

This is most of the reason why laptops die.

As far as I know, by far the most popular reason for laptop death is a liquid spill.

Yep, the whole reworking tired solder joints thing mostly came from 2 sources. Shitty Xbox360 thermals and a whole generation of Nvidia graphics where the chip-package interface died of thermal stress becuase the rest of the package design wasn't up to the job. Leaving the world of hobbyist meddlers going, "oh no lead free is shit, the joints break" which to the extent they imply it, is total cobblers.

Reflowing double sided boards twice is standard practice, the solder will handle it just fine, the structure changes if the cooling stage is wrong.

[Berni]

This is most of the reason why laptops die.

As far as I know, by far the most popular reason for laptop death is a liquid spill.

Well yeah that, and being dropped on the floor. But i meant as the reasons that are not a fault of the user or some outside evil like a lightning strike, so death of non-abused laptops.

But its not like every single joint would die after a few years of thermal cycling. It just gets more brittle to make it more likely to fail.

A good example of failiure due to thermal cycling are CFL bulbs used outdoors. They don't tend to have a very long lifespan (They see a lot of cycling due to how hot they get). If you open one up after it has failed you can often pull troughhole components off the board using just pliers. You just grab a diode and pull hard with a bit of wiggling and the component pulls straight out, leaving the rest of the solder joint on the PCB pad with a hole in the middle where the pin used to be.

[Rat_Patrol]

I still have 15 year old laptops running XP (reasons for custom, old software that I need) that still run fine. They are Dell business laptops though...

[ar__systems]

I still have 15 year old laptops running XP (reasons for custom, old software that I need) that still run fine.

And? That proves something?

[Rat_Patrol]

I still have 15 year old laptops running XP (reasons for custom, old software that I need) that still run fine.

And? That proves something?

Just the whole BS of bad solder joints killing laptops.

[ar__systems]

I still have 15 year old laptops running XP (reasons for custom, old software that I need) that still run fine.

And? That proves something?

Just the whole BS of bad solder joints killing laptops.

Just because your one laptop still works means the issue can't be real? That's funny.

[MR]

15 years old notebook? good chance that the thing is soldered non lead free and that's a whole different story.
The regulation came in in 2006 as far as I remember.

[S. Petrukhin]

Ttell me peaxe what kind of glue is used for SMT, how it is pumped and how it is dried?

[Kjelt]

Ttell me peaxe what kind of glue is used for SMT, how it is pumped and how it is dried?

Usage:
https://www.nexpcb.com/blog/how-to-use-smt-red-glue

Glue Example:
https://www.tme.eu/nl/details/sma10sl/chem-preparaten-voor-soldeerwerken/electrolube
https://www.tme.eu/Document/76b970d9ad6397ec1b1f12184a86d97e/SMA.pdf

[S. Petrukhin]

Ttell me peaxe what kind of glue is used for SMT, how it is pumped and how it is dried?

Usage:
https://www.nexpcb.com/blog/how-to-use-smt-red-glue

Glue Example:
https://www.tme.eu/nl/details/sma10sl/chem-preparaten-voor-soldeerwerken/electrolube
https://www.tme.eu/Document/76b970d9ad6397ec1b1f12184a86d97e/SMA.pdf

Thank you for the information. As far as I understand, applying glue requires a separate machine for its dot dosage and this machine requires a separate file of coordinates and sizes of the glue spot. Or the glue can be applied via a stencil, but then applying solder paste via the stencil will become impossible and soldering must be performed in a wave?

[Kjelt]

Yes AFAIK the solderpaste is stencilled and the glue is dispensed with a syringe and pressure being a cnc machine with airpressure or manual.

[Smashcat]

There are no more fixed profiles included, but I did make setting up custom profiles a bit easier, along with a lot of other UI changes and additions 😁