Hello everyone! This project introduces the implementation of "DIY SMT induction", which is made of a cloth ferrite and is fixed to the thick copper plate using the melting point of the solder paste to achieve heating requirements of heat transfer.
The goal of making this DIY SMT induction is very simple, easy to make, material affordable and can support the normal operation of the machine.
Project Video:
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Component list:
Iron element 700W-1000W (I used to recover the old iron)
Copper plate 150mm x 250mm x 2.2mm
Wooden board 460mm x 380mm x 20mm
M4 screw 50mm long
M4 bolt
AC power cord
Anti-static pad 145mm x 345mm
The rest is used to prepare the temperature sensor:
PCB (provided by JLCPCB)
OLED display SSD1306
Atmega328pu
16MHz crystal
22PF CAP 0603 package
10K resistance 0805
NTC 10K
5V 1A charger circuit
3D print housing / box
Irrigation agent (epoxy resin and hardener)
Teflon, black, white
Reflow welding PCB
Solder paste
Arduino is set as an ISP programmer
Production steps:
Step 1: About the welding paste
The melting temperature of the solder paste depends on the percentage of flux and the ratio of Sn-Pb, the ratio I use is 63/37, that is, SN63-PB37. The melting point of the Sn-Pb solder is from 140 to 270 ° C.
Note - You need to check the melting temperature when you purchase solder paste. Use a low melting temperature of solder paste. (170-200 ° C)
Step 2: Basic settings
The heating plate is powered directly from the AC power supply without adding a relay to the heating plate line to cut off the power or control. The reason is very simple, adding the relay in this setting means that we need to observe the temperature and turn off the heating plate when the heating plate reaches a certain temperature, and then reconnects when the heating plate temperature drops.
On the components of the iron, there is a mechanical component, ie thermostat.
The thermostat is an important part of the electric iron to adjust its temperature. When the iron reaches a certain temperature, the thermostat closes the power of the iron. The mechanism consists of a double metal strip made of brass and iron. When the temperature of the iron exceeds a certain limit, the belt begins to bend to the metal at a lower expansion coefficient. As a result, the strip is no longer physically connected to the contact point, the circuit is turned off and the current stops flowing.
Because the iron has already had a power cut-off circuit for controlling the temperature of the Iron, we only need a temperature monitoring setting to display the accurate temperature of the copper surface.
In order to measure temperatures above 150 ° C, I prepared a NTC-based ATMEGA328PU setup program that displays hot plate temperatures on the SSD1306 OLED display.
Step 3: Prepare the temperature sensor settings
In order to make this temperature sensor setting, I use 10K NTC and Arduino Nano to set the basic temperature sensor settings in accordance with this guide. Setting NTC is very easy, we only need to connect NTCs with the same resistance (10k in me) according to a given schematic.
After completing the bread version, I prepared the minimum atmega328pu setting by using PCB in other projects. I prepared PCB in the PCB Design software, then handed it to JLCPCB for sampling!
I first added the necessary SMD components on the PCB, which is mentioned above. Now, the PCB I use is not used for the branch point of the OLED display, so I have modified the PCB by cutting the copper walking of the four connector, and then adds VCC, GND, A4, and A5 pins to pass the jumper. Connect to the connector. After that, I added THT components, such as IC and insurance. Next, I removed the OLED from previously produced bread board settings and connect it to the current settings with 10K NTC.
The final step is to load Flash BootLoader in Atmega328PU and upload the code in it. To do this, I use the Arduino As ISP programming board, which is Arduino nano that flashs Arduino as a ISP sketch. We can refresh the microcontroller by connecting the SPI pin of the ISP programmer with the SPI pin of the target microcontroller. Then the bootloader of the Atmega328PU is burned and load it uploaded. The final result is that the DIY temperature sensor shows the real-time temperature measured by NTC.
Step 4: Construction of the induction furnace element
The main part of the project is an element setting. We can put the PCB directly on the surface of the iron, which will reflow the PCB without problems, but the surface area of the iron is not enough to reflow the large PCB, to increase the reflux surface, I purchased a sized copper plate with a size of 150mm x 250mm x 2.2mm.
My plan is to add a copper plate on an iron element. Copper has very good thermal conductivity, so it is very suitable for the project. I use M3 screws to drill the mounting holes on the iron components and copper plates. I fixed them, and then the huge heating plate is installed. Three wells are used to fix iron elements with copper plates, and the four holes are used to add copper plates to the wooden base.
Step 5: Prepare base materials such as base
As for the base, the wooden board I use is 460mm x 380mm x 20mm. I have drilled the mounting holes on the wooden base according to the hot plate, and then use the M4 screw, washer and bolts to secure the MIDI Copper board to the air away from the surface of the wood. But before I tighten them, I applied paint on the wooden board and added an ESD mat.
I don't need to add an ESD mat, I added it because it has heat resistance and after reflowing any PCB, we can place PCB (still in hot) on the mat and the mat will not melt. I use rubber binders to connect ESD mat to the wooden base.
Finally, I added an AC connector to connect the HotPlate AC power to the AC cable. In order to secure the AC power cord in the appropriate position, I added a plastic component to secure the power cord to the appropriate position. After setting the base to the hot plate, I added a temperature sensor setting with a screw on the base. Now, for NTC settings, we need 5V current, and this setting runs on the AC power. In order to obtain direct current from the AC power supply, I used a 5V 1A charger circuit and designed a custom fuselage.
I used white PLA 3D to print the body and prepared an epoxy resin mixture for potting the entire box to make DIY isolation 5V power supply!
Step 6: Epoxy resin potting process and complete
When the substrate is placed in a pot, the potting process is started. The liquid compound is then poured into the pot and filled with it and completely covered the equipment. Liquid is hard, encapsulates the equipment (in this example for AC-DC charger circuit) I poured epoxy and curing agent into two different paper cups (30 ml per 30 ml), and mix them Together. EPOXY RESIGN maintains liquid, but when the curing agent is added, its ingredients begin to change and solidify.
After mixing the epoxy and curing agent, I put the charger circuit in its 3D print body and poured the mixture into it. After a few hours, it was completely cured, and finally got this rugged and isolated 5V power supply. According to a given schematic, I will connect this pot power supply to the temperature sensor settings and AC power, and our settings have been basically completed!
Step 7: SMD Process and PCB Reflow Process
Reflow welding is the most widely used method that connects surface mounting elements to printed circuit boards (PCBs). The purpose of this process is to form an acceptable solder joint by first preheating the component / PCB / solder paste, then melting the solder without overheating. In order to make the final check, that is, some of the PCBs are reflow, I will use these two PCBs, they come from two projects before!
Attiny85 GameBoy
2. Nanoleaf project
I designed these PCBs in Orcad rhythm and then sent them to JLCPCB for sampling.
The first step is to add a solder paste by a suitable solder paste to each pad.
I used a broken tweezers to scrape rarely from the solder paste cartridge, I have to add a solder paste to each component pad, because the PCB needs very little. SMD component
The ideal method is to use Stencil, you can also get STENCIL from JLCPCB, another method is to use a decent solder paste dispenser, the solder paste dispenser requires another type of solder paste, which contains a large amount of flux in the solder paste. . The flux reduces the hardness of the solder paste. (As for me, the solder paste is very hard)
Next, we must place the components in the specified location by means of sharp tweezers. I am using the 10K ohmic resistance of the 0805 package, and the 1K resistance of the 0603 package, as well as the indicator LED with the same package, and the A7 diode.
Now, we need to lift the PCB and put it on the heating plate. Turn on the electric furnace and wait a few minutes.
After a few minutes, the PCB starts heating with the temperature rise. When the temperature reaches the peak of 270 ° C, the solder paste is completely melted. I have done the same process for Nanoleaf PCB.
I added a solder paste on the LED pad, which did take time and effort, but after completing the hard work to add solder paste to each pad, I put the SMD WS2812B LED in their designated position. And put the entire PCB on the hot plate for reflow process results very good.
Step 8: Conclusion, limitations and defects, and improvements
The resulting induction cooker that finally produces is indeed working properly and is ideal for PCB reflow soldering for the project. It can even reach a temperature of 300 ° C, can even be used for reflow metal PCB, in general, I am satisfied with the results. The hot plate is working fine, but after the heat plate reaches 270 ° C, the temperature sensor setting does not work properly, which may be because I use 10kNTC. I have already ordered 100K NTC.
The hot plate currently requires a reliable temperature sensor setting, and if the DIY temperature sensor does not work, the appropriate panel temperature sensor module can be used here, and the cost is about 15 to 20 dollars, but even at a higher temperature. Displays an accurate temperature reading.
In any case, this is like this for Part 1. I will make the necessary changes in this Hotplate project, and adjust it in Part 2 of the project, so stay tuned!
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