Surface-Mount Technology (SMT) — how are devices installed on the PCB? With modern SMT assembly practices, how should the devices be attached relative to the printed circuit board?

Introduction / Context:
Surface-Mount Technology (SMT) revolutionized PCB assembly by eliminating the need for component leads to pass through holes. This question checks your understanding of how SMT parts are installed compared to older through-hole practices.

Given Data / Assumptions:

• Context: standard SMT manufacturing with solder paste, reflow, and solder mask defined pads.
• Components: SMD packages such as 0603 resistors, SOIC, QFN, BGA.

Concept / Approach:
Through-hole components require drilled holes; SMT devices are placed directly onto copper pads on the PCB surface and soldered (often by reflow). No component lead insertion is needed. Mechanical retention and electrical connection come from the solder joints on the surface pads.

Step-by-Step Solution:
Identify SMT hallmark: components are placed on surface pads, not into plated-through holes.Consider manufacturing steps: apply solder paste to pads, place components, reflow to form joints.Therefore, SMT devices mount directly on the PCB surface.

Verification / Alternative check:
Inspect any SMT board: you will see flat solder joints and no leads protruding through the board. Packages like QFN/BGA can only be surface-mounted.

Why Other Options Are Wrong:

• Utilize transistor outline connections: TO packages are typically through-hole or bolt-down, not SMT by default.
• Have parallel connecting pins: vague and not defining SMT assembly method.
• Require holes and pads: this describes through-hole technology, not SMT.

Common Pitfalls:

• Assuming SMT always replaces through-hole; in mixed technology boards both may coexist.
• Confusing SMD package shapes with mounting method.

Final Answer:
mount directly