DIY SMT Hotplate Project
Introduction: DIY SMT Hotplate Project
Hey Everyone what's up!
So this is my "DIY SMT Reflow Iron" made from Cloth Iron Element screwed onto a thick copper plate to transfer heat for achieving the desired heating which would be the correct melting temperature of Solder paste (which is in my case 270°C)
The goal for making this DIY SMT Reflow was simple, it's easy and cheaper to make a working SMT Reflow Hotplate instead of buying a proper hotplate.
Video-
Supplies
* Iron's Element 700W-1000W (I'm Reusing this from an OLD Iron)
* Copper plate 150mm x 250mm x 2.2mm
* Wooden Board 460mm x 380mm x 20mm
* M4 Screws 50mm Length
* M4 Bolts
* AC Cord
* ESD Mat 145mm x 345mm
The rest of the parts are for Preparing the Temperature sensor.
* PCB (Which was Provided by JLCPCB)
* OLED Display SSD1306
* Atmega328PU
* 16MHz Crystal
* 22pF Cap 0603 Package
* 10K Resistance 0805
* NTC 10K
* 5V 1A Charger Circuit
* 3D Printed Enclosure/BOX
* Potting Compound (Epoxy and Hardener)
* Teflon wires RED, Black, White
* PCB for Reflow
* Solder paste
* Arduino as ISP Programmer setup
Step 1: Little About Solder Paste
The Melting Temperature of solder paste depends on the Flux percentage and the ratio of Sn-Pb which in my case is 63/37, Sn63-Pb37.
Sn-Pb solder has melting points from 140 to 270 °C higher.
Note- I bought this Solderpaste without checking the Melting temperature. Solder paste with a lower melting temperature should be used. (170-200°C)
Step 2: Basic Setup
The hotplate is powered Directly from the AC Supply, no Relay has been added to the hotplate line for power cutoff or Control. 472
The reason for this is pretty simple, adding Relay to this setup means we need to monitor the temperature and cut the supply of Hotplate whenever the hotplate reaches a certain temperature and then reconnect when hotplate temperature goes down.
On the Iron's Element, there's a mechanical part in iron which is the thermostat.
The thermostat is an important component of an electric iron that regulates its temperature, when Iron reaches a certain Temperature, the Thermostat turns off the power of iron. This mechanism consists of a bimetallic strip that is made from Brass and iron, when the temperature of the iron exceeds a certain limit, the strip begins to bend towards the metal with a lower coefficient of expansion. As a result, the strip ceases to be physically connected to the contact point, the circuit opens and the current ceases to flow.
you should definitely check out this great article about the working process of iron from here for more detail about the Iron's working!
So the bottom line here is that the iron already has a Power Cut Off circuit that controls the temperature of Iron, we only require a Temperature monitoring setup that displays the accurate temperature of the Copper surface.
For measuring Temperatures higher than 150°C, I Prepared an NTC Based Atmega328PU Setup which displays the Hotplate Temperature on an SSD1306 OLED Display.
Step 3: Preparing the Temperature Sensor Setup
In Order to Make this temperature Sensor Setup, I used a 10K NTC along with an Arduino Nano to set up a basic Temperature Sensor setup by following this Guide.
Setting up NTC is pretty easy, we just need to add NTC with the same Value resistance (in my case 10K) in series with the NTC according to the given schematic.
* After Finalizing the Breadboard version, I prepared a Minimal Atmega328PU Setup by using a PCB from a different Project.
PCB that I'm using here was from a Different project which was this-
https://www.instructables.com/Arduino-Based-Synth-With-Mozzi-Library/
I prepared the PCB in a PCB designing software and then gave this PCB to JLCPCB for samples!
* I first added the necessary SMD components to the PCB which were mentioned in the schematic above.
* Now, the PCB that I'm using doesn't have a breakout point for OLED Display, so I modified the PCB a little bit by cutting the copper traces of Four connectors and then I added VCC, GND, A4, and A5 Pins separately to that connector by jumper wire.
* after that, I added THT Components like the IC and burge strip. 472