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Printed circuit boards

Printed circuit boards are in use in almost all electronic devices. Except for the smallest electronic devices, Printed circuit boards are found in all electronic devices. This article will discuss quality control in printed circuit boards to bring the reader to the understanding of quality control in PCBs, how printed circuit boards are manufactured, the materials used, and the justification.

Why laminate materials?

Circuit Board Manufacturing and PCB Quality Control Methods

What Is Quality Control, And Why Is It Important?

Quality control is a set of processes designed to ensure that a product or service is done in adherence to the defined quality standards for safety, optimum functionality, and cost-effectiveness.

Standards are often approved by a body approved nationally or internationally. For electronics, there are several bodies responsible for setting internationally acceptable standards.

• ISO (International Organization for Standardization), for ensuring standard processes in electronics design and product development.
• ITU (International Telecommunication Union) which regulates telecommunications
• IEC- International Electro technical Commission involved in testing and certifying electrical, electronic, and related products
• IPC (Association Connecting Electronics Industries) which is involved in electronic boards (PCB’s)

IPC standardization process

What is the implication of quality control on PCBs?

PCBs are the backbone of all electronic devices and, therefore, directly impact the quality of performance. PCBs determine the functions and performance of electronic devices. PCBs’ quality control is a continuous process, from the design to the manufacturing process. Now that we understand the design and functions of PCBs, we can now delve into quality control in PCBs and understand the dynamics therein.

There are various aspects of quality control that one can perform on PCBs. as noted earlier, quality control is an ongoing process and can be summarized into the following:

• Incoming quality control is done at the point of entry, where quality checks are done on supplies in line with the required standards and client specifications. There is also the constant review of supplier performance and taking corrective actions.
• In process quality control – refers to the continuous quality checks and procedures that ensure quality flops are caught and addressed before it is too late.
• Final quality control is done at the final stage before products are released to the consumers.

Quality Control in PCB Design

Quality control in design involves the following critical activities;

1. Ensuring the Validity of the PCB design file

A design file is a critical component in quality control, as it is the major communication tool between the fabricator and the designer. Various types of files can be sent to the fabricator containing information on the PCB design. The project leader has to confirm the validity of the design file as a measure of quality. The information contained in the design file translates to the materials that designers will need in manufacturing the particular PCB required. Errors in the design file will have a chain reaction on the entire process and compromise quality.

Types of PCB design files are;

• Gerber files – these are ASCII formatted files containing everything on the PCB layer image, and don’t require external files for extra information.

Gerber files

• IPC Netlist/ IPC – 356 – has instructions for PCB CAM software including net names, start and endpoints for the nets and nodes and locations.

IPC PCB Netlist

• Drill files NC format – these files contain PCB drilling and routing information
• Fab drawing
• BOM (Bill of materials) – this is a list containing information on all parts that are required for building a specific printed circuit board.
• IPC-2581
• Pick and Place files – this is a list of all the components with regard to the specific PCB design. Pick and place files also contain information on the respective x-y coordinates and rotation.

Pick and Place setup

It is also critical to check on;

• Design rule check-list
• Design for manufacturability

Design rule checklist

• Design rule checklist

The process of PCB design and manufacturing involves multiple components and connections. A lot goes on in designing quality PCBs, and given the central roles of PCBs in electronic devices, management of the process cannot be left to chance. A design rule checklist keeps track of all the requirements and dimensional tolerances meant for a specific board. The checklist allows the designer to double-check that every guideline in the design, assembly and manufacturing of PCBs aligns with the design files and the acceptable standards of the different PCBs.

• Design for manufacturability

The design for manufacturability (DFM) approach has become prominent in the quality control process. This is the process through which the design layout is done in a way that foresees and addresses problems in assembly and fabrication. DFM is critical in quality control designed to optimize costs in time for product development, repairs, wastages, and recalls. DFM has two critical components: a design for fabrication, which forecasts problems at the fabrication stage, and a design for assembly, covering issues at the design phase. The DFM process is an important quality control tool.

2. Guarantee the manufacturability of PCBs

PCB manufacturing comes with technological requirements that are governed by standard procedures. Once the design has been approved, quality control checks shift to the availability of the requisite technology to manufacture the specified design. In this phase, the technologist must possess the required skills to manufacture the specified design and possess the right tools for the manufacturing process. The manufacturer should communicate the requirements clearly and reasonably, and the machinery must meet the specified operations standards.

3. Guarantee the testability and normalization of PCBs

The testability and normalization of PCBs must conform to the laid down standards in the industry. The process requires checking and analyzing test points, dimensions, routing, structural style, and testability for manufacturing. Design for testability (DFT) happens before production and is meant to catch testing issues earlier on in the process. The process is meant to catch defective products before production.

Quality Control In Component Procurement

Quality control in procurement is an essential part of ensuring the production of high-quality PCBs. Each component used in PCB manufacturing needs to be of high quality if the resulting product meets quality standards. The following areas are critical in component procurement;

• Validation of the bill of materials (BOM) – the items listed on the bill must align with the final design file.
• Manufacturer part number (MPR) – this is a measure in procurement that allows the purchasing of the right part. The manufacturer gives an MPR
• Visual inspection is done once the components have been received, ensuring that the delivery matches the order.
• Supplier verification – suppliers must be credible and reliable, and their products must meet the industry-accepted standards and guidelines.

Quality Control in Production of PCB

• Manufacturers capability

Before embarking on a project, the designer must conduct thorough investigations on the manufacturer’s capability to deliver quality. The manufacturer must have complied with the standard operating procedures outlined by the regulating bodies.

• Constant checking and confirmations

Using the design rule checks, design files, and other tools available, the production team is responsible for conducting numerous checks and confirmations before production commences. Since the first design is not always perfect, and there is a need for multiple design files as consultations between the designer and manufacturer ensue, the production team is responsible for confirming the final design file before commencing production.

• Attention to key procedures

Quality control in production defines how key production procedures are carried out. Quality control in the design process is crucial to ensure that each step follows the accepted standards. Key procedures in PCB production are as follows;

• Design imaging is done using a specialized printer, producing photo negatives of the design file or schematic diagram.
• Printing the inner layers on copper
• Ultraviolet light blasting meant to harden the photo reactive photo chemicals
• Inner layer etching
• Aligning the layers
• Optical inspection
• Layer pressing and lamination
• drilling
• PCB plating
• Imaging the outer laying
• Etching the outer layer
• Solder mask application

Soldering mask application

• Silk screening
• Finishing
• Testing
• Profiling
• Final quality check
• Packaging and shipping

There are guidelines to every single process guaranteeing the quality of the final product. Quality control measures in production are a step-by-step process.

Quality Control in PCB Inspection

This is the process of monitoring and measuring PCBs, with strict adherence to quality standards. The final product must reflect the initial design outlined in the design file. There are acceptable quality standards in every industry and country, and quality PCBs must meet these standards in the context they will be in use. Quality control inspection is done in the following ways;

• Visual inspection
• Performance inspection
• Technological inspection

These methods are further broken down into:

• Visual inspection involves a thorough check of connections and other components of the PCBs with the use of the naked eye. This can be applicable where the volume of production is low.

PCB visual inspection

• Microscope – where the naked eye fails, microscopes, USB devices, and handheld visual tools provide a clearer, wider view of the components and possible quality issues.

Man using microscope for visual inspection

• In-Circuit Tests – this method uses electronic inspection methods, a bed of nails, and fixtureless. Bed of nails testing uses pogo pins arranged in a series, pressing into different test points to measure resistance. Fixtureless or flying-probe testing uses probes that are machine-operated. They check test points on the PCBs at breakneck speeds.
• X Rays use non-invasive technology to inspect quality issues in PCBs visually.
• Automated optical inspections use webcams and OpenCV to compare a perfect PCB and the finished product under inspection and point out the discrepancies.
• Functional testing involves full tests on the functionality of the PCB once it has been manufactured. Self-tests run on the PCBs as part of the trial tests.
• Inspection cameras are high-resolution cameras that produce high-quality images. These are projected on screens where operators can view the PCB components with the naked eye and perform necessary inspections.

What is the most reliable method of quality control before assembly?

Electrical testing is the more reliable testing method for PCBs before shipping. There are two major ways of testing PCBs before assembly;

• Universal grid test
• Flying probe test

Universal grid test/bed of nails

This method uses pins mounted on an epoxy surface, and these numerous pins are inserted into the holes. These are aligned into the testing point, allowing the testing to be done simultaneously.

Flying probe test

A generic board holder contains one or more that are controlled by software to test for opens and shorts, as well as test other things.

Quality Control Methods

There are several methods one can use to guarantee quality to their customers and reduce the cost of recalls, expensive lawsuits, and other negativities associated with low quality.

• IPC certification
• Component expertise
• Process controls
• Assembly checks
• Inspection and tests
• Functional workspace

IPC Certification

IPC standard is a globally recognized trade association that involves itself in standardizing the manufacturing of PCBs electronics components. These standards also regulate the assembly, protection of electronic equipment, training, research, and advocacy on public policy.

The IPC offers continuous development programs on PCB. IPC certification is based on industry standards, and practitioners in the field must be certified by the IPC for soldering, reworking, and assembly of PCBs. The certification must be up to date, and compliance with the industry standards must also be on display and up to date. IPC certification controls operations standards and ensures the same standards are maintained across the industry, leading to safe, reliable, and quality PCBs. IPC gives the following benefits of adherence to their quality standards and quality control measures:

• The product becomes reliable and high quality
• Reduced costs due to recalls, wastages and damage through faulty equipment
• Improved communications
• Better relations with customer and and management

IPC defines quality in the following three classes, that define the quality of the electronics (class 1 contains products with the least quality while class 3 has items with the highest quality;

• Class 1 – in this class, the major requirement is the functionality of the complete IPC assembly, and contains the equipment contained here are the general electronic equipment and everyday products
• Class 2 contains products like laptops. The equipment here are for dedicated service, and must have highly reliable and has extended life to qualify for this class.
• Class 3 contains high performance electronic products. These must perform on demand, sometimes with no equipment downtown. Some of the equipment belonging to class 3 are life support systems and other medical equipment.

IPC standards are meant to cover design, production and assembly of PCB as a measure to control quality. These standards are as listed;

• IPC-A-610 – it covers the acceptability of electronic components, and clearly outlines the prerequisites for acceptability.
• IPC-A-600 – is all about the acceptability of printed boards
• J-STD-001 – outlines the soldering requirements of electrical and electronic components
• IPC-7711/IPC-7721 instructs on how to rework electronic components/printed board, repair or modify electronic components.

Standards are built on conditions that define and justify the quality control process. IPC has the following conditions;

• Target Conditions – refers to goals that are set as a reference point for every PCB manufacturer. The objective is to ensure the manufacturers produce PCB that are as close as possible to the target products.
• Acceptable Conditions are the ideals which PCB products ought to meet in quality and in design. PCB manufacturers are meant to meet the conditions, with a negligible margin of error allowed.
• Defect Conditions address and define what is categorized as defective inPCB manufacturing. Defective products are reworked or rejected.
• Process Indicator Conditions don’t affect performance or quality of the end product. They however impact on selection of materials, design parameters, manufacturing and assembly.

Component Expertise

The engineering process and inspections should be in place to ensure the use of only the best parts for the job. The engineer should possess vast knowledge of the different components for producing the specific PCB. Some factors to consider when investigating the expertise of the engineer is how well they understand;

• Power consumption and alternatives parts that can help you stay within the budget without compromising on quality;
• Type of memory for your device
• Different internet protocols compatible with the device design
• Simulation protocols
• Mixed-signal design

Usually, understanding these different components, applicability, advantages, and disadvantages give you confidence in the quality of the product.

Process Controls

Process control entails the following;

• Documentation is an important part of process control. A professional will have documented procedures and processes that adhere to the standards of operation as guided by the regulating body. Documentation of processes is a great way to forecast results and detection of anomalies early enough.
• Constant monitoring during manufacturing regulates process control, and once any anomaly is detected, the process is immediately re-adjusted to the required cause. Process controls ensure process uniformity across all production units and uniformity of products.

Assembly checks

PCB assembly process

Assembly checks involve the checking of solder points before and after soldering. The process is as follows:

• Solder paste – solder paste is added to requisite areas before adding the components on the board. The solder paste amount is controlled to ensure only the right amount is used. ‘
• Pick and place – this is the process where the board with the solder paste is picked by a machine with a series of reels and placed at the right place on the board. The solder paste holds the components in place.

 

A pick and place machine

• Soldering – this is the process of passing the board through the soldering machine, mostly through reflow soldering techniques.
• Inspection – once the soldering process is done, the boards undergo inspection as part of quality control by automated inspection. The inspection process is automated to inspect boards for poor joints and misplaced components. In some cases, faulty components are detected during the inspection process.
• Testing – inspection is followed by testing. Testing is an integral part of all development of electronics and electrical components. The following are some of the popular instruments used in testing;

1. Multimeters,
2. analog and digital (DMM – digital multimeter),
3. Oscilloscopes,
4. spectrum analyzers

Inspection and testing

• A manufacturer should document inspection and testing methods and provide documented evidence on previous work done.
• The inspection and testing methods should align with the industry best practices and should be up to date. Inspection and testing procedures are inbuilt and part of every process.
• Functional workspace – quality standards reflect on the working space, evident in the assembly down and individual working space organization.

Quality control in workspaces is determined by;

• Building proper processes, done through documentation, clear labeling of equipment, organization, and smooth working procedures
• Clean workspaces
• Unscheduled equipment use tests – it ensures quality is maintained at all times, as surprise breakdowns of machinery are reduced to a minimum,
• They are identifying essential spare parts and ensuring their availability at all times.
• Proper staff training and refresher courses keep the staff updated on the latest industry standards and requirements.

Conclusion

PCBs are critical components of electronic devices and are expected to be of the highest quality standards achievable. Quality control processes are indispensable, especially in PCBs. Quality control ensures quality PCBs are produced in line with industry standards. Producers and consumers greatly benefit from quality control, as they avoid unnecessary costs in recalls and wastages brought about by faulty pieces of equipment. Adherence to quality standards guarantees a competitive advantage for manufacturers and customer satisfaction, a prerequisite for higher profits. High-quality PCBs guarantee the safety of electronic equipment around the world. The compromised safety of PCBs would pose a great danger to humanity.

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