Hey guys. This here is a low-cost reflow hot plate for SMD components and is homemade.
If you remember, a few weeks ago I’ve made another reflow hot plate using a clothes iron
of 3000W, a solid-state Relay with and Arduino and other components. That works great but
it was a bit expensive, is too big for me and also it has way too much power for what
I need. This time I’ve used this small heating plate that costs around 7 dollars. And the
rest is also very low-cost. A few dollars for the Arduino, the screen and the relay,
a few more dollars for small components such as buttons, the switch, a fan and wires and
the case is 3D printed. I’m sure that you wonder if the plastic case goes well with
the heating plate. Well, it dose and I will explain you in this video how I’ve designed
the case in such a way that the heat from the plate will never reach the plastic case
and it’s quite interesting. I will show you all the components you need, how to assemble
everything and we will make some tests with a few PCBs. So, what do you think? Will this
project be able to reflow my PCBs? Stick till the end to find out. So, let’s get started
What’s up my friends, welcome back. Let’s go over the part list first and then we make
the project, we go over the code and finally we test it. So, what we need. Well, remember
that in my previous reflow hot plate project, I was using this clothes iron as a heating
plate. This has a lot of power, a lot more than we need, especially if we use low temperature
solder paste. The problem with this was that measuring the temperature was a little bit
difficult and slow. And why was that? Well, because first, I was using a thermocouple
with this amplifier module. This module could send a measurement only each 200ms so if you
need faster reading, well you can’t. And second, the heat propagation was quite slow
so till the real heat was reaching the thermocouples, the PID was already way behind so we always
had over temperatures so I had to adjust the values manually. This time I will use this
heating plate that I bought from AliExpress for just a few dollars. I still want to keep
this project low cost so it would be cheaper than buying a reflow station. This plate has
an internal heating resistor of around 450 ohms, so at 360V it could deliver around 280W
of power which is 10 times less than the other project if you remember, that one was 3000W.
On AliExpress, the plate was marked as 400W but I’m not sure that it could reach that.
Anyway, I’ve realized that we don’t need more than 3 hundred watts. Is made of aluminum
which will transfer the heat very fast. To control the power, we need a solid-state relay.
You could use a big one like this one as I’ve used before, but this time, since we have
less power, I will use one like this one that could work at 220V and could deliver 2 amps
of current. It could also be easily controlled with an Arduino. So, obviously, we also need
an Arduino which in this case, I will use again the Arduino NANO. To show the values
I will use an LCD screen with the i2c communication module so is easier to control. This time
I will use the 16 by 2 one instead of the 20 by 4 one as in the previous project. To
measure the temperature, I will now use a thermistor instead of a thermocouple. This
is just a simple resistor that will change its value according to the temperature so
is very easy and fast to read compared with a thermocouple, and we will see how in a moment.
We also need to sue a fan like this one, and you will see why when we assemble the project.
The heater works at 220V but the rest of the digital part is working at 5V. So, to lower
the voltage to 12V I will use this small converter. We can connect this to the Vin pin of the
Arduino, and since this already has a 5V regulator, that’s how we get our 5V for the rest. To
turn the entire circuit on and off I will use this switch which also has an integrated
LED and that’s nice to have. I also want to add a buzzer like this one for alarm notifications.
Finally, to assemble the case you will see that we need some sort of metal plate. I will
use this one and when we assemble the project I will explain why. Finally, for the case
it would be better to make it out of metal but my workshop is not prepared for working
with metal yet. That’s why I’ve made my design out of plastic. This was printed in
ABS so it will withstand more heat. The heating plate will stay here and it will never be
in direct contact with the case. Also, the only way to transfer heat to the plastic case
would be thought these screws that we add below the plate. And because they are long
enough, the heat will transfer slowly. Even more, these screws will be connected to that
metal plate I’ve told you before and only this plate will be in contact with the case.
This plate will dissipate the heat even more and below we will have a cooling fan. Between
the heating plate and the metal plate I also want to put some of this heat insulation cotton.
This should protect the case even more from the heat of the top plate. And above all that,
remember that our solder paste melting point is 172 degrees and you could also find some
paste that will melt at 138. This temperature is still ok with ABS that melts at around
230 degrees or more. The case has a few parts and I’ve designed in such a way that everything
will fit perfectly. On this small part we add the screen and the buttons. So we also
need 4 of these type of push buttons. On the side of the main case we have a space for
the on and off switch and on a back we have a space for the cooling fan. The metal plate
will get screwed inside here and we have a small plastic skirt around so it will keep
it at that exact height. On the bottom part we can screw the PCB with the Arduino and
the relay on the side. That’s pretty much it. It took me a while but finally, I had
a good design. So this is all that we need for this project so let’s assemble it. But
please be careful, this project is working with high voltage from the main outlet so
if you’re not sure don’t start this project. Also use proper insulated tools and never
touch the exposed wires. Download this schematic from below and have it in front of you so
you can follow the same steps. First we need to secure in place the heating plate. For
that we need to add the metal plate below because if you will try to add it later, you
won’t be able because we will have these plastic parts that will get in your way. So
we must add it first. Inside we have 4 holes for screws. Make sure you add holes to your
metal plate as well. 4 holes fort the heating plate screws and 4 more holes on each corner
for the plastic case screws. Add the plate and tight the screws on each corner like this.
Now take the heating plate and add 4 long screws and tight a nut for each like this.
At this point we also have to secure in place the thermistor on the metal plate so we can
measure the temperature. We can use this kind of thermistor or this one that already has
a metal cover and like that maybe it will have better connection. But in my case, since
I still have a little bit of space aside of the heater element inside, I will add my thermistor
inside here. I secure it in place with force and some KEPTON tape that could withstand
very high temperatures. Then we add 4 more nuts that will define the maximum height.
Before I add the heater inside, I cut some of this insulation foam. I cut it to size
and also make holes for the screws. Then I add it in place over the metal plate. Now
I add the heater and make sure you pass the power wires and the thermistor to the bottom
side because the electronics will eb below here. From below I tight 4 more screws and
the heater is in place. As you can see, the plate gets a little bit above the plastic
case so we can easily remove our PCBs. Now let’s assemble this part. First, we have
to add the push buttons. So, get 4 button and solder wires to each like this. One black
wire for ground and a color one for signal. Each button will go behind this plastic pad.
Like that, when we push the pad, we will push the button as well. To keep the buttons in
place I’ve printed this part that will get screwed here and support the buttons. So I
decide where each button will ho and then I glue them to that small support part. Now
I screw the support in place with some very tiny screws. Now when I push the plastic pad,
the button is pressed, as you can see, we can hear the click. Now we add the LCD in
place. I add some screws and tight some nuts so we have some clearance. Then I add the
LCD and add more nuts to keep it in place. Remember to also solder wires for power and
the i2c communication. Now I get the relay, a prototyping PCB and the bottom 3D printed
part. I screw in place the relay. Now I measure where the PCB will go in order to be screwed
on these 4 holes and I cut it to size. With the PCB in place, I decide where to place
the Arduino and the 5V converter and also some outputs and inputs. I solder the Arduino,
the regulator and the buzzer in place and 4 sets of pins for the LCD, buttons, the fan
and the thermistor. On the back I make the connections with thin wires and some thicker
wires for power. Let’s make a small pause and let me show you how to read a thermistor.
As you can see, at room temperature its resistance is 10K ohms in this case. I have other models
that have 100K ohms. Anyway, when I heat it up, its resistance will go lower. If I connect
this thermistor in a voltage divider with another resistor with a known value, I can
measure the voltage change at the output and using a graph, I can measure the temperature.
As you can see here, I have the thermistor and another 10K resistor in a voltage divider.
I supply it at 5V and measure the output. As you can see, when I heat the thermistor,
the output will change. All I have to do, is to sue the Arduino analog pin and measure
this voltage and using a graph like this one, we can precisely know the temperature. So,
as you can imagine, this is way faster and easier than using a thermocouple but we can
go to very high temperatures. Let’s resume the assemble. I get the on and off switch
and solder 3 wires and the one with the LED also has a resistor to limit the current.
I add this switch on the side of the case. Then I screw in place the cooling fan and
make sure it will suck the air in. I get the power cable and pass it through the hole on
the back and make a knot inside and also add some glue so it will stay in place. Finally,
I make all the connections as in the schematic. Main power to the switch and from here we
supply the relay and the 5V converter. The relay will then supply the heating plate and
so on. Everything is connected. Is time for the code so download it from below and upload
it to the Arduino. In the code we set the loop refresh rate with these lines. Then we
read the temperature using a library for thermistors. According to the elapsed time and the real
temperature, we control the PID code that will control the power of the Relay. What
we try is to follow this curve here which is the melting curve of the solder paste.
We apply the PID output to the Relay with a PWM signal and this will try to keep the
power in such a way that the temperature will follow the setpoint. Once the code passes
over all the stages, it will start the cooldown, and also ring the buzzer a few times in order
to let the user know that the process is over but the plate is still hot. That’s pretty
much what the code dose. I’ve uploaded the code and made sure the temperature control
is ok and also tried different PID values till I’ve got decent results and I was closer
to this curve for my solder paste. Now that the code is uploaded and we know it works,
we can close the case. Take a few of these insertion nuts. Using your soldering iron,
we insert them int the holes of the plastic case. As you cans see, we only have holes
on two corners. The other two will be added using these parts. We have one for each corner
and they will stay in place with the same screws we use to connect the LCD part to the
main case. So using two screws we make a sandwich between the LCD part, the main case and these
small parts for the screw. Once they are in place, I use my soldering iron once again
ad add two more insertion nuts. Now we can add the bottom part and close the entire case
and the project is ready. It looks quite good right? But dose it work? Connect it to power
and flip the switch. The internal LED of the switch should turn on indicating that power
is connected. The LCD will also start and tell the user to select a mode. On the screen
we can see temperature, if the relay is ON and when the mode is running, we can see the
setpoint, the PWM value and the elapsed time in seconds. I prepare a testing PCB with some
solder paste and I add a few components using the tweezers. I place the PCB over the heating
plate. From the menu I select mode 1, which is the only mode for now, and I press run.
We start with the ramp where we go up to 150 degrees, then the soak part and finally we
go above that temperature and reflow the components. With the first test I had too much solder
paste so the components merged together so I had to make another proper test. Once the
components are soldered, we enter the cooldown mode. At this point you can remove the PCB
from the plate. The cooldown mode will end when we get below 40 degrees. For the second
test I’ve used a solder paste stencil to apply the correct amount of paste. This time
as you can see, we have the correct amount. Now that we have good solder paste, I add
the components again using tweezers. I put the PCB on the hot plate and run mode 1 again.
The reflow process was OK but some components moved so I had to use the tweezers and put
them in place. But in overall, the reflow process was a success. I’ve made another
test with another PCB and I’ve also placed a PCB on the side with only the solder paste.
As you can see, the one without components started to melt faster. Then we can see all
the components getting soldered. The project is a success. So guys, what do you think?
The entire project is quite low-cost since the heating plate was just a few dollars,
the Arduino, the relay and the small components as well and the case is 3D printed. You have
the full part list and the prices below in the description. So, do you like my project?
If so, comment below or give this video a like
Thanks again and see you later guys.