Motor control PCB is an essential in our daily lives. This type of PCB serves a great role in the operation of a myriad of devices we depend on every day.
Any propulsion system, including electric cars, airplanes, fuel pumps among others, virtually depend on motor controller circuit board to operate efficiently.
This guide will answer some of the importance you may be having on motor control PCB.
Let’s dive right in.
A motor control PCB is the heart of any motor controller device. It helps in regulating the motor speed, torque and equipment output.
There are 4 primary types of motor controller that must incorporate motor control circuit board:
Also known as adjustable frequency drives, variable speed drivers, or AC inverters, AC motor controllers alter the input voltage to motors. The attain this by modifying the frequency of energy going into the motor, thus regulating the torque and speed.
DC motor controllers, similar to AC motor controllers, also change input power. They alter the input current to direct current output, and regulates the speed and torque of the motor efficiently.
A servo motor controller alters the input power through regulation of the source of current to required current, pulse, or frequency output. These motor controllers are perfect for specific applications.
Servo motor controllers are ideal for use in motion control applications, particularly in construction and manufacturing sectors. They control motor speeds, torques, and positions.
Stepper Motor Controller PCB
Also called motor indexer, this motor controller type regulates input power through adjustment of source of current to stepped current output. Stepper motor controllers are also perfect for construction and manufacturing industries.
Similar to other types of motor controllers, stepper motor controllers regulate the speed, torque and position of the motor.
Generally, an inverter-based motor controller PCB system comprises of a:
Block Diagram of Components of Motor Control PCB
There are three key principles by which motor controller PCB device operates:
H bridge circuitry, which features four switches regulated in pairs, is the simplest mechanism of controlling DC motor.
When the circuit closes either of the switch sets, they complete the circuit instantly and eventually power the motor. Motor controller PCB with H-bridge may control the motor speed as well.
H Bridge Motor Controller Circuit Board
PWM circuitries vary the motor speed through simulating a reduction or increase in voltage supply. Pulse width modulation is simple and affordable to implement, an attribute that facilitates continual regulation of the speed of motor.
Here, the motor control PCB incorporates variable speed drive controllers, which operate by relaying cyclical impulses to the motor. These pulses make the coil inductance to cause binding smoothing effect.
This is another mechanism of modifying the speed of DC motor, where you vary the input current either via field or armature coil.
There will be change in output shaft speed with change in coils current. Variable resistors can alter the current to enable you increase the motor speed.
Here are the common IC packages you will use in motor control PCB manufacturing:
TSSOP packages come in rectangular shape and utilize 2 rows of pins. The TSSOP packages applied in motor control PCB assembly often feature a massive bare pad underneath the package. The exposed pad helps in heat dissipation from the package.
TSSOP Package for Motor Control PCB
On the other hand, QFN packages refer to leadless packages with pads about the exterior edges of the device. They also have bigger pad at the center of the package that helps in heat dissipation from the die.
QFN Package
To dissipate heat from QFN package, you must make a properly-soldered connection to the bare pad. Often, the exposed pad is at ground potential, therefore, you can attach it to the ground plane of motor control PCB. Basically, thermal vias are located in the pad section directly.
Ordinary leaded packages, such as SOT-23 and SOIC packages are usually employed for low-power motor control PCB devices. To optimize the power dissipation capacity of the packages, apply “flip-chip on lead-frame” structure.
In this construction, you bond the die to the metal leads utilizing solder and copper bumps without using bond wires. This facilitates conduction of heat from the die via the leads to the motor control circuit board.
Flip-on-Chip Leadframe Construction
To optimize thermal performance, attach wide copper areas to the leads carrying high current. Typically, the output, ground, and power pins are connected to copper areas on motor controller PCB.
FCQFN packages resemble conventional QFN packages. However, rather than utilizing wire bonds for die to pads connection, you flip the die upside-down and attach to pads below package directly.
FCQFN Package
You can locate the pads adjacent to the heat-producing power elements on the die. Therefore, they are usually placed as long stripes rather than small pads.
The Flip-Chip QFN packages utilize copper bumps rows on the die surface that are eventually fixed to the leadframe.
Flip-Chip QFN Construction
QFN and TSSOP packages feature a big exposed pad underneath them. Linked to the back of the die, this pad helps in the transfer of heat from the IC package.
Therefore, it is essential you solder the pad properly to the motor control PCB to effectively dissipate heat.
The opening within the stencil used for depositing solder paste for the exposed pad is not usually designated on the IC package datasheet.
Normally, SMT process engineers apply their own rules on the quantity of solder to deposit and pattern type to employ on the stencil.
When one opening with size equal to the pad is used, you will deposit large quantity of solder paste. This can lead to lifting up of the package because of surface tension when the solder melts.
Another challenge is solder voiding (gaps or cavities within solder areas). Solder voiding takes place when the volatile flux component vaporizes during the process of solder reflow. This can result in forcing of solder from the joint.
To solve these problems, for exposed pads over ~2 mm2, the depositing of paste is usually in various small circular or square areas. Portioning the solder paste into smaller segments enable volatile flux constituents to more effortlessly escape without dislodging the solder.
Component placement instructions for motor control PCB ICs are the same as those for other power IC types. You should install bypass capacitors as close to power pins of the package as practical, with bulk capacitors positioned nearby.
Many motor controller PCB ICs utilize charge-pump capacitors and/or bootstrap, which you also need to place close by the IC package.
While featuring a continuous, broad plane minimizes thermal resistance, copper thickness on the plane is equally important in motor control PCB thermal performance.
Increasing the copper plating thickness on the circuit board reduces the plane’s effective thermal resistance.
Copper makes an excellent heat conductor, hence, in terms of thermal management, you should have more copper area on your motor controller PCB.
Thick copper, like 36 microns (2-ounce) foil, is better in heat conduction than thinner copper. Regrettably, thick copper is considerably costly and challenging to attain fine geometries with.
Generally, 34 microns (1- ounce) copper is standard, particularly for circuit boards having 0.5mm pin pitch or lower. For external layers, you can use ½-ounce copper that can be plated up to thickness of 1-ounce.
Solid copper planes utilized on the inner multilayer motor control PCB layers disperse heat well. Nonetheless, because these planes are usually located in the middle of the circuit board stack-up, heat may be trapped within the PCB.
To disperse heat from the planes, you can add copper coverage on the external PCB layer.
Additionally, you can place many vias to stitch, or connect the areas that trap heat to the internal planes.
On two-layer motor control PCBs, dispersing heat may be more challenging because of presence of components and traces.
Therefore, it is necessary to provide more solid copper having perfect thermal interconnections to the motor control circuit board.
Placing copper pours on either external layers and joining them using several vias helps disperse heat through sections cut by parts and traces.
In motor control PCB design, multiple vias are normally utilized for high current interconnections between layers. Using multi-vias is not only essential in high current connections, it also helps in low parasitic grounding.
It is important to give correct quantity and dimensions of via to attain low resistance and prolonged reliability. Generally, the via diameter ought to at minimum be the trace length.
When utilizing copper plane as trace, you should locate the multi-vias near the current’s entry or exit from the component pins.
Motor Control PCB Assembly
You must correctly size the width of motor control PCB traces. This is because of its large input and output current (surpassing 10A in certain instances).
Wider traces have lower resistance therefore, you should size traces to ensure there is
