The Step-by-Step Guide to Printed Circuit Board Assembly and Testing

August 27, 2025

The Step-by-Step Guide to Printed Circuit Board Assembly and Testing

Printed circuit board assembly (PCBA) is the heartbeat of any modern electronic device. From aerospace systems to consumer electronics, a well-assembled and tested PCB ensures optimal performance, product longevity and customer satisfaction.

At ACDi, we’ve spent over 40 years refining the PCBA process—applying our expertise to deliver high-reliability, on-schedule builds that meet rigorous industry standards like AS9100D and ITAR compliance. Whether you’re new to electronics manufacturing or looking to optimize your supply chain, this guide walks through the complete PCB assembly and testing process—from bare board to final inspection.

Step 1: Design File Review and DFM Analysis

Before assembly begins, we review the Gerber files, Bill of Materials (BOM) and assembly drawings to verify manufacturability. This Design for Manufacturability (DFM) review helps catch issues early, such as:

Component spacing violations
Unclear polarity markings
Inaccessible test points
Part obsolescence or mismatches

ACDi Value Add: Our in-house layout team can work closely with customers to optimize layouts for cost, performance and long-term component availability.

Step 2: Component Procurement

Once the files are approved, we procure components from authorized distributors (specified in your BOM), ensuring traceability and quality. Our supply chain team focuses on:

Avoiding counterfeit parts
Substituting end-of-life components
Verifying Moisture Sensitivity Level (MSL) ratings
Managing lead times and lot tracking

Pro Tip: For defense and aerospace applications, we ensure parts comply with relevant standards and certifications.

Step 3: Solder Paste Application

Using automated stencil printers, we apply solder paste to designated pads on the bare PCB. This solder paste acts as the bonding agent for surface mount components.

Key considerations:

Precision in stencil alignment
Paste viscosity and volume control
Environmental conditions like temperature and humidity

Step 4: Pick and Place Component Placement

Surface mount technology (SMT) machines place components on the paste-covered pads with extreme accuracy—sometimes over 50,000 placements per hour.

Fiducial marks guide component alignment
Cameras verify correct orientation
Vacuum nozzles handle parts from 01005 up to large ICs

ACDi uses multiple SMT lines to support both high-mix, low-volume and high-volume, low-mix production.

Step 5: Reflow Soldering

After placement, boards travel through a reflow oven, where controlled heat melts the solder paste, creating strong electrical and mechanical bonds.

Temperature profiles are carefully tailored based on:

Board size and thermal mass
Solder type (leaded vs. lead-free)
MSL component profiles

ACDi follows JEDEC J-STD-020 guidelines to prevent issues like popcorning or delamination.

Step 6: Inspection and Quality Control

Once reflowed, we inspect the boards using:

Automated Optical Inspection (AOI): Detects solder bridges, missing components, tombstoning and polarity issues
X-ray Inspection: For BGAs and other hidden joints
Manual Microscopy: For edge-case verification or complex parts

Our IPC-certified technicians verify assemblies against IPC-A-610 standards.

Step 7: Through-Hole Component Insertion (if applicable)

If the design includes through-hole components (like connectors or transformers), these are inserted manually or with automated insertion equipment.

They are then soldered using:

Wave soldering (for bulk processing)
Selective soldering (for tight spacing or heat-sensitive areas)
Hand soldering (for prototypes or low volumes)

Step 8: Final Cleaning and Conformal Coating

After assembly, PCBs may be cleaned to remove flux residues or contaminants. For harsh environments, conformal coatings or encapsulation are optionally applied to protect against moisture, dust and corrosion.

Common materials include:

Acrylics
Silicones
Polyurethanes

Some test is done prior to conformal coating and then again after, such as functional test, while flying probe is done before.

Step 9: Electrical Testing and Validation

Testing ensures the board functions as intended. ACDi offers multiple test options based on the complexity and end-use of the product:

In-Circuit Testing (ICT): Verifies individual components and connections
Flying Probe Testing: Ideal for low-volume or prototype builds
Functional Testing (FCT): Simulates real-world operation
Boundary Scan/JTAG: For testing inaccessible nets
Burn-In Testing: For mission-critical or high-reliability applications
Environmental Stress Screening (ESS): Can include shock, vibration, temperature, altitude, humidity, etc.

All test data is logged and traceable to support root-cause analysis or regulatory compliance.

Step 10: Final Inspection, Packaging and Shipping

Before shipment, each PCB or assembly is subjected to:

Final visual inspection
Labeling (including serial numbers, revision levels, date codes)
Custom packaging solutions (ESD-safe bags, foam inserts, etc.)

Our logistics team ensures your assemblies arrive safely, on time and ready for integration.

Why Choose ACDi for PCB Assembly and Testing?

40+ years of electronics manufacturing experience
In-house layout, assembly, and testing
AS9100D certified
ITAR registered
Domestic U.S. manufacturing with flexible volume capability
Turnkey or consignment options

Ready to Simplify Your PCBA Process?

Contact ACDi to discuss your project or request a quote. Visit www.acdi.com to learn more.

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