From SMT to BGA: Essential PCB Assembly Terminology and Engineering Trade-offs

In hardware design and manufacturing, professional terminology forms the foundation of communication and decision-making. The choice of a "via" type can directly impact BOM costs by 30%, while overlooking the assembly nuances of a "BGA" may lead to catastrophic field failures. To successfully bridge design and volume production, it is essential to thoroughly understand the relationship and technical requirements between a PCB  and a PCBA (PCB Assembly). This article not only explains key terms (like SMT, DIP, THT, SMD, BGA, COB,  Blind via, Through hole, Buried Via, AOI, X-Ray, ICT, FCT ) but also delves into the core engineering trade-offs that affect product reliability, manufacturability, and total cost.

1. SMT vs. THT: Choosing Between Foundational Processes

Surface Mount Technology (SMT)

SMT is central to modern electronics miniaturization. It uses Surface Mount Devices (SMDs), soldering components directly onto PCB pads. This typically saves 60–70% of board space, enables higher-density designs, and suits automated, high-speed production.

Through-Hole Technology (THT)

THT requires component leads to be inserted into drilled holes in the PCB and soldered. Although bulkier, it remains indispensable in specific scenarios.

The Engineering Trade-off: Choosing between SMT and THT is fundamentally about balancing space efficiency, production cost, and mechanical/electrical reliability.

2. Core Component Packages: Characteristics and Risk Awareness

SMD (Surface Mount Devices)

SMD Refers to various surface-mount components. Smaller sizes (e.g., 0402, 0201) demand higher placement accuracy and carry increased risk of defects like "tombstoning" during reflow soldering.

BGA (Ball Grid Array)

BGA packaging is the mainstream choice for high-density integrated circuits. Its solder joints are located beneath the chip, providing hundreds of I/O connections in a very small area.

COB (Chip-on-Board)

COB packaging bonds bare dies directly to the PCB. It minimizes product profile and cost but results in a non-repairable design, typically used for high-volume, low-cost consumer products.

3. PCB Structure Essentials: The Design Philosophy of Vias

Vias are electrical pathways connecting different layers of a PCB. Their type directly influences stack-up design, routing capability, and manufacturing cost.

4. Quality Assurance System: A Multi-Layered Inspection Defense

AOI (Automated Optical Inspection)

Uses high-definition cameras to quickly detect 2D defects such as placement errors, reversed polarity, and solder bridges. A standard configuration for SMT lines.

ICT (In-Circuit Test)

Uses a bed-of-nails fixture to verify the electrical performance of on-board components (e.g., resistor values, shorts/opens), ensuring correct soldering and component values.

FCT (Functional Circuit Test)

Simulates the product's real operating environment to verify full board functionality. Serves as the final verification step before product release. Try NextPCB free functional test service.

X-Ray Inspection

Primarily used to inspect the solder joint quality of hidden terminations like BGAs and QFNs. An essential method for ensuring the reliability of high-density packages.

About the Author

Julia Wu - Senior Sales Engineer at NextPCB.com

With over 10 years of experience in the PCB industry, Julia has developed a strong technical and sales expertise. As a technical sales professional, she specializes in understanding customer needs and delivering tailored PCB solutions that drive efficiency and innovation. Julia works closely with both engineering teams and clients to ensure high-quality product development and seamless communication, helping businesses navigate the complexities of PCB design and manufacturing. Julia is dedicated to offering exceptional service and building lasting relationships in the electronics sector, ensuring that each project exceeds customer expectations.

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