Cost effective Precision based Surface Mounting Device SMD for PCBs

Assembly of components onto the Printed Circuit Board (PCB) uses mainly two techniques; the first, more prevalent method being the one that employs through-hole technology and the second, relatively advanced method employs Surface-Mount Technology (SMT). As no component leads must be inserted throug

Project Title

Cost effective Precision based Surface Mounting Device SMD for PCBs

Project Area of Specialization

Robotics

Project Summary

Assembly of components onto the Printed Circuit Board (PCB) uses mainly two techniques; the first, more prevalent method being the one that employs through-hole technology and the second, relatively advanced method employs Surface-Mount Technology (SMT). As no component leads must be inserted through holes in the PCB during assembly, Surface Mount Devices (SMDs) are well suited for high speed, reliable placement, miniaturization and low cost.

The SMD assembly process can be classified in three categories: Picking (the component is picked with a vacuum), Alignment (of the component relative to the board), and Placement. The accuracy with which components are to be placed on the PCB is a very crucial step in the assembly process, before these steps are executed small amount of solder paste is applied on the copper pads of the PCB where the component is placed.

The system has been modelled according to the following schematic:

Figure 1: Schematic for System Model of Cost-effective and Precise SMD on PCB.

The body of the machine comprises primarily of four axis, X, Y and two Z, that are to be controlled using a MACH-3 controller connected to a computer. The X and Y axis have screw rods that travel using Nema-17 stepper motors. The two Z axis are made of linear sliders mounted on the travelling plate of the X axis. Two Z axis are being used according to our design; one for paste dispensing and the other for the P&P action.

The P&P machine was programmed with the information about component positions, developed through Gerber File. The machine, after determining the position of a component by converting the Gerber file to G-code, picks up electronic components, ICs, from the feeder tray (holds the components before they are placed onto the PCB). The ICs are picked through the vacuum nozzle connected to a hollow shaft, Nema-8 stepper motor through a header. Before the IC is placed onto its respective position on the PCB, a drop of high-quality solder paste is dispensed onto the corresponding location through a pressure control kit with its air outlet connected to a syringe.

The design for this model also includes two cameras mounted on the machine. One camera has been placed between the two Z axes to help with the precise placement of the components on the PCB. The other camera is faced upwards and has been installed on the platform. It is used to correct the orientation of component in the case that it is not deposited in the correct position from the feeder tray. Both the cameras have been programmed using computer vision principles through OpenCV.

Figure 2: Flow of processes taking place on the proposed SMD.

The code for the microcontroller, object detection and scaling programs have been written and tested through python (OpenCV). Detection of the corner points and the center of the IC was a crucial step for their precise placement on the PCB.

Project Objectives

We aim to meet the following objectives:

1. Cost-effective
2. High Precision
3. Long Life Cycle
4. Compatible with different operating systems
5. Little maintenance expenses
6. Reduced labor

In terms of technical objectives, we hope to achieve the following targets by the end of March 2020:

1. Accurate Paste Dispensing on the PCB
2. IC size and center calculation using computer vision
3. Accurate Placement of IC on the copper pads.

Although SMT has been around for nearly four decades, Pakistan still lags behind with system upgrades and latest models. The reason for this is mainly due to the high cost of these equipment ranging from 3000 USD to 18000 USD. We as a team aim to manufacture a SMT that would be cost-effective but will not compromise the quality and precision of the work.

Project Implementation Method

Once the user creates a Gerber file it is converted to G-code and added to the source code of the machine, by doing so the machine knows all the positions of the copper pads where the paste is to be dispensed. The paste modules reach all these positions via the X and Y axis and moves up and down by the Z axis. The paste is dispensed using AD982 dispensing kit which is attached to a 12V compressor. The signal to the dispensing kit is sent via the microcontroller using a 5V relay connected to an aux cable.

Once the paste is dispensed the Pick-and-Place (PnP) header moves towards the feeder tray and picks up the required IC, the picking action is possible due to a vacuum controlled by a 5V relay and a 12V solenoid. The IC is placed onto the board assisted by two cameras that help to detect edges of the copper pads and the IC to correct its orientation. The orientation is controlled using a hollow shaft nema-8 stepper motor that allows the vacuum pipe to run through it till the nozzle of the PnP module.

This process is repeated for all the modules on the board and once done the board is heated in an oven up to 200 oC.

The code for the microcontroller, object detection and scaling programs have been written and tested through OpenCV. Detection of the corner points and the center of the IC was a crucial step for their precise placement on the PCB.

This was achieved using Algorithm 1:

Benefits of the Project

The following are the benefits that can be achieved by implementing this project at commercial level

1. Cheap manufacturing of SMT PCB
2. Fast delivery in Pakistan
3. Providing industries in Pakistan a better alternate and reducing imports
4. Better commercial rates can improve competence in foreign market
5. Creating jobs for technically sound and skilled labor

  

For the past two and a half decades, China has been the hub to SMD PCB manufacturing, attracting markets from all over the world with project sizes ranging from domestic uses to international market leaders like Samsung and Apple having their manufacturing units in China.

There are two main reasons why china has been this successful:

1. Cheap labor with basic technical knowledge
2. Manufacturing their own SMD equipment

Though Pakistan fulfills the first criteria, expensive SMD equipment has been a barrier to future development. Companies like Taraz Technologies have got a hold of these equipment but the cost and charges they offer for the services are nearly twice than those offered by Chinese manufacturers like ALL PCB so China is basically getting hold of  the Pakistani market by manufacturing these equipment themselves and selling at a higher rate.

Therefore, what we hope to achieve is to introduce SMD equipment at a much better price than international market leaders but also not compromising the quality of work and the precision with which it is to be done.

This would also mean the work being done in Pakistan does not need to be at halt for weeks while waiting for shipments from China but rather be done in days with the obvious benefit of less cost of production.

Technical Details of Final Deliverable

For the final demonstartion the machine should be able to dispense drops on the copper pads using the G-cde.

After that it would pick up the components from the feeder tray and place them at the correct position.

the position of the copper pads will be deduced by the G-code but cameras will also assist in this work for high precision and accuracy.

The figure shows the 3 stages of a SMD before it is placed in a reflow oven for heating in the 4th step.

Final Deliverable of the Project

HW/SW integrated system

Core Industry

Manufacturing

Other Industries

IT

Core Technology

Robotics

Other Technologies

3D/4D Printing

Sustainable Development Goals

Industry, Innovation and Infrastructure

Required Resources

If you need this project, please contact me on contact@adikhanofficial.com