Printed Circuit Board (PCB) Assembly Services Process - PCBWay

Surface Mount Assembly Process

Originally, all PCBs were assembled by hand using only a solder iron. As technology progresses, components get smaller and more difficult to assemble by hand and the amount of components that may fit on a single board increases. Thus the need for auto assembly was developed.

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Required Elements

The following are the required elements for auto assembly:

• Gerbers in 274-X (embedded apertures) including fabrication drawing.

• Part centroid text file with Reference Designators, external placement layer, and X & Y location and rotation in ASCII format.

• Numerical control (NC) drill files

• Solder paste file (one of the Gerber files) for all sides mounted

• Glue dot file

• If possible, the design database, specifying the database format (program name)

• Parts list or BOM (bill of material)

• Parts or hardware required

The Gerber files are used to define the pad locations and help the assembly house determine where pin 1 is located and provides a heads-up of how the board looks. The database can also be used to determine the location of pin 1. Some board houses choose to make their own solder paste file/stencil. The designer may create the solder paste file to his/her own preference with experience. It is good to learn how and why the assembly house makes its stencils and duplicate it to ensure consistency from each assembly house (the common name for any company that assembles boards). The solder paste file is used to mask the entire board except those areas that will be soldered. Solder paste is applied to the exposed pads and the stencil is removed. Components are applied and held to the board by the solder paste and the glue dots securing the components as they are soldered to the board.

For component placement a part placement/centroid file is required to know where the center of the part is. The layer ID shows what side the part is placed on, and the rotation displays the orientation of the component.

Consistency in rotation of the original component is critical to report. Unless the designer's software can account for inconsistencies, all components should be created in the same orientation.

NC drill files are used to locate mounting holes and provide the holes sizes for thru-hole components. This also allows the assembly house to determine adequate clearance for the component lead.

A bill of material or parts list is used to reference the designators of the centroid file and the components that need to be mounted. The BOM should also provide information if the component is an SM component or a thru-hole component.

Other Considerations

Other considerations for auto assembly are the board size, the panel size, and breakaways. The boards are commonly assembled in a panel that may contain many boards. The panel is the original material that the boards were etched routed in. The panels pass to the assembly house with all boards intact.

Note

Breakaways are the connections around a board that hold the board during assembly but can be broken easily when it is time to remove the board.

1.Ordering a Board

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2.DFM Check

The DFM check looks at all the design specifications of a PCB. Specifically, this check looks for any missing, redundant or potentially problematic features. Any of these issues may severely and negatively influence the functionality of the final project. For example, one common PCB design flaw is leaving too little spacing between PCB components. This can result in shorts and other malfunctions.
By identifying potential problems before manufacturing begins, DFM checks can cut manufacturing costs and eliminate unforeseen expenses. This is because these checks cut down on the number of scrapped boards. As part of our commitment to quality at a low cost.

3.Incoming Quality Control(IQC)

PCBWay Verifying all incoming materials and handling quality problems before subsequent SMT assembly begins. Our IQC position will check following issues of incoming materials if they comply with our strict requirements.

• model number and quantities according to BOM list

• shape (deformation, broken pin, oxidation etc), particularly for IC or other complex components

• sample test of incoming materials by tools such as test frame, multimeter etc.

• If above defect or discrepancy occurs, we will return full incoming materials to supplier or customer.

4.Machine programming - Gerber / CAD to Centroid / Placement / XY file

Having received the PCB panels and components the next step is to setup the various machines used with the manufacturing process. Machines such as the placement machine and AOI (Automated Optical Inspection) will require a program to be created which is best generated from CAD data but quite often this isn't available. Gerber data is almost always available as this is the data required for the bare PCB to be manufactured.

5.Solder Paste Printing

The first machine to setup in the manufacturing process is the solder paste printer which is designed to apply solder paste using a stencil and squeegees to the appropriate pads on the PCB.

6.Component Placement

Once the printed PCB has been confirmed to have the correct amount of solder paste applied it moves into the next part of the manufacturing process which is component placement. Each component is picked from its packaging using either a vacuum or gripper nozzle, checked by the vision system and placed in the programed location at high speed.

There is a large variety of machines available for this process and it depends greatly on the business to what type of machine is selected. For example if the business is focused around large build quantities then the placement rate will be important however if the focus is small batch/high mix then flexibility will be more important.

7.Pre-Reflow Automated Optical Inspection (AOI)

Following the component placement process it is important to verify that no mistakes have been made and that all parts have been correctly placed before reflow soldering. The best way of doing this is by using an AOI machine to make checks such as component presence, type/value and polarity.

8.Reflow Soldering

Once the components are placed on the boards, each piece is sent through our reflow machines. This means the solder paste needs to solidify, adhering components to the board. PCB assembly accomplishes this through a process called "reflow".

This would appear to be one of the less complicated parts of the assembly processes but the correct reflow profile is key to ensure acceptable solder joints without damaging the parts or assembly due to excessive heat.

When using lead-free solder a carefully profiled assembly is even more important as the required reflow temperature can often be very close to many components maximum rated temperature.

9.Post-Reflow Automated Optical Inspection (AOI)

The last part of the surface mount assembly process is to again check that no mistakes have been made by using an AOI machine to check solder joint quality.

Often, movement during the reflow process will result in poor connection quality or a complete lack of a connection. Shorts are also a common side effect of this movement, as misplaced components can sometimes connect portions of the circuit that should not connect.

Checking for these errors and misalignments can involve one of several different inspection methods. The most common of these inspection methods include the following:

• Manual Checks
• Automatic Optical Inspection(AOI)
• Automated X-ray inspection(AXI)

10.Conformal Coating

Some completed Printed Circuit Board Assemblies have a conformal coating. It's usually depends on the customer's product requirements.

11.Final Inspection and Functional Test

After the soldering and conformal coating step of the PCB assembly process is finished, a final inspection will test the PCB for its functionality by our Quality Assurance team. This inspection is known as a "functional test". The test software and tools are usually provided by the customer, PCBWay can also make fixtures according to customer requirements. The test puts the PCB through its paces, simulating the normal circumstances in which the PCB will operate. Power and simulated signals run through the PCB in this test while testers monitor the PCB's electrical characteristics.

12.Washing and Drying

Suffice it to say, the manufacturing process can be a filthy one. Soldering paste leaves behind some amount of flux, while human handling can transfer oils and dirt from fingers and clothing to the surface of the board. Once all is said and done, the results can look a little dingy, which is both an aesthetic and a practical issue.

13.Packing and Shipping

All assembled boards are packaged (can request in anti-static packaging) and shipped DHL,FedEx,UPS,EMS,and so on. Any unused components are returned in accordance with customer instructions. Additionally, customers are notified via when their packages ships.

Introduction

Printed circuit boards (PCBs) are the backbone of modern electronics. From smartphones to computers to medical devices, PCBs provide the foundation on which components are mounted and connected. As electronic products become more advanced, PCB design and manufacturing has grown increasingly complex. This has led many companies to outsource PCB assembly rather than maintain these capabilities in-house.

Choosing the right printed circuit board assembly (PCBA) partner is critical to the success of your product. This guide will provide a comprehensive overview of PCBA services, factors to consider when selecting an assembly provider, key steps in the PCBA process, and strategies for ensuring quality outcomes. Gaining insight into PCBA best practices can enable your company to get products to market faster and more cost-effectively.

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Overview of Printed Circuit Board Assembly Services

PCB assembly, also known as PCBA, involves soldering and assembling electronic components onto a PCB. While some companies still assemble PCBs in-house, most now work with specialized contract manufacturers that offer PCBA services. The key benefits of outsourcing PCBA include:

• Cost savings - Contract manufacturers can achieve significant economies of scale across their operations, reducing assembly costs.
• Specialization - Leading contract manufacturers invest heavily in advanced assembly technologies and employ skilled technicians. This expertise is difficult for individual companies to develop and maintain internally.
• Speed - Large-scale contract assemblers have the capacity to rapidly scale production, helping meet demand and launch products faster.
• Quality - Reputable partners adhere to rigorous quality control standards in order to deliver high yields and function.
• Flexibility - Contract manufacturers offer services globally and can adjust to changing production requirements.

In addition to assembling PCBs, contract manufacturers often provide related services:

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• PCB fabrication
• Component sourcing and procurement
• Inventory and warehouse management
• Testing and inspection
• Packaging and order fulfillment
• Reverse logistics and repair

By leveraging these capabilities under one roof, customers can streamline their supply chains and product development cycles.

Key Factors in Selecting a PCBA Partner

Choosing the right contract manufacturer is perhaps the most important decision in the PCBA process. Here are key factors to consider during selection:

Technical Capabilities

• What assembly technologies do they offer (through-hole, surface mount, etc.)?
• Can they work with the latest component packaging types?
• Do they have experience with your product type?
• Do they assemble flex, rigid-flex, and other PCB technologies?

Quality Processes

• Are they certified to key quality standards like ISO , IATF , or AS?
• Do they have rigorous quality inspection procedures?
• How much process documentation and traceability do they provide?

Supply Chain Management

• Can they procure necessary components and manage inventory?
• Do they have preferred supplier relationships?
• How is counterfeit component risk mitigated?

Reliability and Accessibility

• Do they consistently meet on-time delivery targets?
• How transparent are they about production timelines and issues?
• Can they scale rapidly while maintaining quality levels?

Location

• Where are production facilities located relative to your team or target markets?
• Do they have language resources aligned to your needs?
• What are their export control capabilities?

Cost Structure

• How flexible are their pricing models (fixed-price, time & materials, etc.)?
• What are their minimum order quantities and volume tiers?
• Are they willing to provide cost transparency?

Customer Service

• How responsive are their sales and engineering teams?
• Will they assign dedicated account management staff?
• Do they take a collaborative, solution-oriented approach?

You'll want to evaluate partners on all the above criteria through a formal request-for-quote (RFQ) process. Site visits to prospective manufacturer facilities are also recommended whenever possible.

Key Questions to Ask Prospective PCBA Partners

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• What technologies and processes do you use for SMT assembly? Through-hole assembly?
• How do you inspect PCB assemblies after production?
• How do you test assembled boards before shipment?
• What data and documentation will I receive on my board assemblies?
• How do you qualify and monitor your component suppliers?
• What counterfeit avoidance measures do you have in place?
• What are your capabilities for assembling and testing high-speed, high-complexity designs?
• How do you ensure the security and confidentiality of customer data?
• What systems and certifications do you have for quality management?
• How do you guarantee on-time delivery for orders?
• How will you keep me updated on order status and any production issues?
• What support do you provide for new product introduction and ramp-up?
• Do you help optimize designs for manufacturability and cost?
• What IT infrastructure enables collaboration and data exchange with customers?
• How can I regularly monitor process performance metrics?

PCBA Process Step-By-Step

Once you have selected a contract manufacturer, efficient execution of the PCBA process is key to achieving a timely, high-quality outcome. Here are the major steps:

Sourcing Components

The contract manufacturer will source all required components for assembly based on your bill of materials (BOM). Reputable partners have established procurement pipelines to acquire authorized components efficiently. Some key considerations around sourcing include:

• Lead times - Confirm that longer-lead components are ordered in time.
• Authorized distribution - Ensure components are purchased through authorized channels, not brokers.
• Allocation risks - Watch for any constrained components that may be put on allocation by suppliers.
• Cost optimization - the assembler can help identify component substitutions that meet spec at lower cost.

Incoming Components Inspection

All incoming components need to undergo inspection:

• Verification - Confirm components match what was ordered on documentation.
• Visual inspection - Check for damage, defects, or abnormalities on each component.
• Dimensional checking - Validate component dimensions are within toleranced ranges.
• Functional testing - Validate basic functionality for certain complex ICs or modules.

This helps catch counterfeit, damaged, or out-of-spec components before they enter assembly.

Solder Paste Stencil Creation

The solder paste stencil is a thin metal sheet laser-cut with apertures matching the PCB footprint. It is laid over the PCB to apply solder paste precisely before component placement. Quality stencil fabrication and inspection helps ensure reliable solder joints post reflow.

Solder Paste Printing

Solder paste is printed through the stencil apertures onto PCB pads using an automated print machine. This deposits small bricks of solder paste where components will be placed. The stencil is cleaned and inspected between every print cycle.

SMT Pick-and-Place

SMT components are autonomously picked from feeders and precisely placed onto PCB pads using high-speed pick-and-place machines. Accuracy of a few microns is standard. Most SMT lines feature multiple placement heads for high throughput.

SMT Reflow Soldering

The PCB passes through a reflow oven to heat solder joints over liquidus temperature. This "reflows" the solder to form reliable electrical and mechanical connections. Different solder alloys, paste formulations, and profiles are used depending on component types.

Through-Hole Insertion

Some components like connectors or fasteners are inserted into plated through-holes in the PCB. This is done manually or via automated insertion equipment. Leads are bent outwards to anchor the component.

Wave Soldering

The underside of the PCB passes over a wave or fountain of molten solder. This solders through-hole component leads. Nitrogen blanketing prevents oxidation. Some boards also pass through selective wave machines that only solder specific areas.

Conformal Coating

A protective polymer coating may be selectively applied over the PCB assembly, leaving connectors exposed. This "conforms" to the board topology and prevents shorting, leakage currents or corrosion.

AOI and Testing

Every PCB assembly is put through automated optical inspection (AOI) and testing procedures:

• AOI checks for defects like missing or misaligned components, insufficient solder, board damage, and more.
• In-circuit testing (ICT) validates electrical performance and catches hard faults.
• Functional testing confirms the board executes properly and meets specifications.

Box Build Assembly

For full box-build assembly, the contract manufacturer can integrate the PCB assembly into the full product enclosure with additional components and wiring.

Final Packaging and Shipment

Assembled boards are packaged based on your requirements, labeled with necessary documentation, and shipped via your requested transport.

Ensuring Quality Outcomes

To achieve your quality and reliability objectives using third-party assembly, keep these best practices in mind:

• Perform regular process audits - Routinely verify that your CM follows agreed process controls. Review solder profiles, inspection records, test data, etc.
• Implement statistical process control (SPC) - Analyze process performance metrics over time to catch deviations quickly. Common metrics include defects per million opportunities (DPMO), yield, test pass rate, and more.
• Get IPC certification - Having IPC-certified staff demonstrates assembly process capabilities. IPC-A-610 sets soldering and acceptability standards.
• Validate and document tooling - Ensure all assembly tools are validated as capable of meeting specifications. Retain documentation.
• Conduct sample audits - When taking delivery of finished assemblies, fully inspect and test a sample to catch any issues before receiving the full lot.
• Manage component life cycles - Work with your CM to monitor end-of-life notices and make last-time buys for obsolete components requiring redesign.
• Regularly review corrective actions - Any major defects or escapes should lead to defined containment actions and permanent corrective actions (PCAs). Review effectiveness of PCAs with your CM.

By combining robust quality frameworks with hands-on process verification, companies can feel confident in outsourcing PCBA while still meeting their product requirements.

Conclusion

As PCB assembly becomes more complex, partnering with specialized contract manufacturers enables access to advanced manufacturing capabilities, economies of scale, and technical expertise. However, the process requires careful vetting and management. This guide provides a starting framework for PCBA service evaluation, partner selection, process oversight, and quality assurance. By investing the time upfront to find the right partner and put disciplined governance in place, R&D teams can accelerate development cycles and focus their energy on design innovation rather than manufacturing operations. With a rigorous approach, contract assembly enables companies to deliver high-quality, field-reliable products in a timeframe that supports business success.

Frequently Asked Questions

Q: What documentation do I need to provide to a contract manufacturer for PCBA?

A: Typical documents provided for assembly include:

• Bill of materials - List of components, quantities needed, part numbers, suppliers
• PCB fabrication and assembly drawings
• Schematics
• Approved vendor list
• Solder paste stencil and solder data sheets
• Product specifications
• Any required testing instructions

Q: How can I ensure the security of my intellectual property when using a contract manufacturer?

A: Protect IP by having a non-disclosure agreement (NDA) in place. Only provide necessary documentation. Use component reference designators rather than names. Secure any software code or firmware. Routinely audit their security practices.

Q: What is the typical lead time for PCBA production?

A: Lead time depends on factors like order size, production scheduling, and component availability. Typicalassembly lead times range from 2-8 weeks. Work closely with your CM on component procurement to avoid delays.

Q: What standards apply to PCB assembly quality?

A: Key standards include:

• IPC J-STD-001 - Requirements for soldered electrical and electronic assemblies
• IPC-A-610 - Acceptability of electronic assemblies
• IPC- - Qualification and performance of rigid printed boards

Q: Can I easily switch between contract manufacturers if needed?

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