PCB Tinning, Description:
PCB Tinning & how to apply Solder to PCB Traces in Eagle– I have these two PCBs with standard 1.6 mil copper thickness. The one on the right side is without the solder and has no soldermask or (solder mask) applied to the PCB traces. This is basically a relays based H-Bridge which I designed to control small DC motors. This is the same circuit that I used in the solar tracker project. While the left side PCB has the Blue color soldermask and also the solder is applied to the PCB traces. Now we will be practically testing if PCB tinning really makes any difference. I will also explain how to manually apply solder to PCB traces to increase the current rating of the PCB traces of your choice. This manual method of PCB tinning may be quite tedious if you have hundreds of these PCBs which need to be tinned.
Isn’t it cool if the PCB manufacturing company like the PCBWay or any other Company do it for you? Of course it is cool, you get PCBs with solder applied to the power lines. But the question is how you tell them which PCB traces need to be tinned? You will get answer to this question while designing a PCB and of course I will explain how to apply solder to the PCB traces of your choice using the cadesoft eagle schematic and PCB designing software.
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Now we will practically test if it really worth tinning the PCB traces. I am going to run this motor using these two PCBs, and let’s see what happens?
I started off by placing the components and completed the soldering job. I carefully soldered all the components and using the digital multimeter I checked the continuity and short circuit. This is how both the relay H-bridge modules looks.
First I will start with the circuit with no solder applied to the traces. I solder the remaining wires for the motor, power supply, and Arduino.
Over here I connect the 12V power supply for the relays, both the relays are of the type SPDT “single pole and double throw”. The Grey wire will be connected with the Arduino’s ground. These two wires will be connected with the Arduino’s I/O pins, I will use pin number 2 and pin number 3 on the Arduino. So, using these two wires we can control the direction of rotation of the DC motor. These two wires on the bottom side are used to connect the external 12V power supply for the 12V DC gear Motor.
With these two points we will connect the DC motor, so let’s go ahead and solder the two wires of DC motor.
You can see the Arduino is turned ON, the DC gear motor is connected with the relay H-bridge. The 12V external power supply is connected which is used to power up the DC motor. I have also connected a potentiometer which I am going to use to control the DC motor. These are just the basic connections, after performing the tests I will share with you the final circuit diagram, PCB board file and Arduino code, the download links are given below. Now let’s start the testing, first let’s check if the whole system really works, using the potentiometer we can control the direction of rotation and we can also turn ON and turn OFF the motor. For the testing watch video tutorial given at the end of this article. While controlling the motor nothing happened to the circuit, because right now there is no load on the motor and draws around 1 to 1.5 amps. The external power supply I am using right now can supply current up to approximately 2amps. It’s really hard to stop this motor with bear hands I am doing this to put some load so that the motor can draw more current.
Next I started with plier but nothing happened to the circuit, because the power supply couldn’t deliver more current. These motors when on load can draw more than 6amps. To increase the current I decided to connect it to a 12V battery. So, I connected two wires from the Battery, now the motor can draw more current. This time it’s hard to stop this motor with plier as the battery can deliver enough current and then a few moments later I could see the smoke.
This trace is damaged, for small dc motors with current requirement up to 4amps this circuit can be used without any problem. Now I will run the same DC motor on the other relay H-bridge circuit with solder applied to the power traces.
I am using the same exact connections, let’s compare this with the other circuit.
During the last test this trace was damaged, while in this circuit solder is applied to the power traces, so hopefully this wont damage.
First let’s check if this circuit really works, I controlled the direction successfully which means the circuit is ready for the test. For the practical demonstration watch video given at the end of this article. Now to put some load on the motor I will use the Plier, I performed the same tests as I did on the previous relay H-bridge. This is really a power full motor, I couldn’t even stop it with the Plier. I kept applying the force, the traces are not even warm, I kept performing the tests, even the Plier was damaged, temperature on the motor side started to increase, but nothing happened to the circuit. So, after performing a series of tests, I must say PCB tinning really make difference. You can increase the current rating of the PCB traces if you apply a thin layer of solder. You can do it manually but it needs some practice. All you need to do is select the proper Soldering iron bit, apply some solder to the bit and then start dragging the bit on the PCB traces.
Be very careful while applying the solder as too much heat can easily damage the traces… Now, I will explain how to apply solder to traces using the Cadsoft Eagle Schematic and PCB designing software.
PCB Tinning in Eagle “Apply Solder to traces in Eagle”:
While your PCB design is opened go to the layer settings and turn ON the tStop and bStop layers.
tStop layer is for the top side PCB and the bStop layer is for the bottom side. If you have a single side PCB then you can select any of these two layers depending on your design whether you doing the designing on the top side or the bottom side.
Anyhow, while the bStop layer is selected, type line or select the line tool, and then start drawing lines on the traces to which you want to apply the solder, it’s just that simple. So, after applying solder to the traces, then you can check your work by disabling the bottom and top layers and you will see traces as you can see in the image given below.
I made it a double side PCB by adding copper traces on the top side as well, this will further improve the current capacity, and also added the solder. Finally I generated the Gerber files. I used the PCBWay online Gerber viewer for checking the Gerber files and once satisfied I placed an online order on the PCBWay official website.
This is the Relay H-bridge module I received from the PCBWay Company. As you can see the quality is really great the silk screen is quite clear and the blue soldermask looks amazing. Now, let’s take a look at the circuit diagram, if you want to learn how to make the relays based H-bridge circuit.
Download Gerber Files:
Relay H-Bridge Circuit Diagram:
This is the circuit diagram of the relays based H bridge module. The normally open and normally closed contacts of both the relays are connected with the 12V battery positive and GND contacts. Another 12V adaptor is used to power up the relays. This is the voltage which is used to energize the relay coil. The two relays are controlled using the Arduino pins 2 and 3.
A Potentiometer is connected with the Arduino Analog pin A0. While the other two legs of the potentiometer are connected with the Arduino’s 5v and ground pins. I have a very detailed article on the relays based H bridge circuit, in which I explained the whole design with the help of Proteus simulation.
Relay H-Bridge Arduino Code:
// H-BRIDGE Code
int relay1 = 2;
int relay2 = 3;
int pot = A0;
pot_data = analogRead(pot);
if ( pot_data < 100)
if ( pot_data > 900)
if ( (pot_data > 100) && (pot_data < 500))
if ( (pot_data > 500) && (pot_data < 900))
Two relays are connected with the Arduino pins 2 and 3. A potentiometer is connected with the Analog pin A0. This is just a basic program. We read the potentiometer and store the value in the variable pot_data. Then we use some if conditions to turn OFF the motor and to control the direction of rotation.
Watch Video Tutorial: