# Surface Mount Technology (SMT)

> Source: https://netray.co/glossary/surface-mount-technology
> Publisher: Netray (netray.co), AI and integration engineering for ERP and manufacturing systems.
> Section: Glossary

## Short answer

Surface Mount Technology (SMT) is the method of placing and soldering electronic components directly onto the surface of a printed circuit board, instead of inserting leads through holes. It is the dominant way modern electronics are assembled.

## Aliases

- SMT
- SMD assembly
- surface mount assembly

## Category

manufacturing

## Full Definition

In SMT, components called surface-mount devices (SMDs) have flat contacts or small terminals that sit on copper pads on the board. A typical SMT line runs in sequence: solder paste printing through a stencil, solder paste inspection (SPI), pick-and-place machines that position components, reflow soldering in a multi-zone oven, and automated optical inspection (AOI). Double-sided boards repeat the sequence for the second side.

SMT replaced most through-hole assembly because parts are smaller, boards are denser, and machines can place thousands of components per hour with consistent accuracy. Through-hole parts still appear for connectors, large capacitors and mechanical stress points, so many boards are mixed technology: SMT first, then wave or selective soldering for the through-hole parts.

From an ERP point of view, an SMT line is a routing of tightly coupled operations, usually one work center per line rather than per machine. The bill of materials can carry hundreds of reference designators per board, and the feeders loaded on the placement machine must match the BOM revision. Machine programs, stencil IDs and oven profiles are controlled alongside the item revision.

ERPs such as Infor SyteLine, Infor LN and NetSuite hold the work order, BOM and inventory transactions for the SMT build, while the line itself is normally driven by machine software and a manufacturing execution system (MES) that reports completions and scrap back through an integration.

## Why It Matters

- SMT yield problems (tombstoning, bridging, insufficient solder) show up as scrap and rework cost that ERP standard costing must absorb.
- Feeder setup and changeover time on an SMT line often decides how small a lot size can be run economically, which feeds lot sizing and scheduling.
- Reel-level component tracking is needed to trace a failing board back to the exact parts and the line that built it.
- Moisture sensitive parts and limited reel shelf life mean SMT planning is tied to purchasing and inventory discipline, not just production.

## In Practice

A 4-layer controller board has 180 SMT placements across 40 unique part numbers. The work order for 500 boards releases kitted reels to the line. The first-article board is inspected, then the lot runs. If AOI flags 6 percent of boards for bridging on one fine-pitch part, the cause is usually stencil aperture or paste volume, and the lot is held for rework before final test.

## Faq

### What is the difference between SMT and through-hole assembly?

**Answer:** SMT places components on the board surface and solders them in a reflow oven. Through-hole assembly inserts leads through drilled holes and solders them, usually by wave or selective soldering. Many boards use both.

### What are the main steps of an SMT line?

**Answer:** Solder paste printing, paste inspection, pick-and-place, reflow soldering and automated optical inspection, with X-ray or in-circuit test added for hidden joints.

### How does an ERP connect to an SMT line?

**Answer:** The ERP issues the work order and BOM, while machine software or an MES reports quantities, scrap and component usage back, typically through an API or file-based integration.

## Search terms

what is SMT, surface mount technology, SMT assembly process, SMT line, SMD vs through-hole, SMT ERP integration

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