Surface Mount Technology: What is SMT?

Surface mount technology components on a narrow circuit board.
Surface Mount Technology components in place. By JCHaywire. CC BY-SA 2.0

Surface mount technology has changed how printed circuit boards are designed. But what do you know about it?

The 1970s and 80s saw a sharp rise in the need for PCBs (printed circuit boards.) To meet that demand, designers had to find a way to manufacture boards more efficiently.

But the traditional way of mounting components–using pre-formed lead wires connected to the board through plated through holes–didn’t allow for fast assembly. Components had to line up at the correct angle before they could mount to the surface, slowing down assembly.

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Circuit Board Reference Designators: FAQs

Circuit board reference designators help identify individual parts on a printed circuit board.
Circuit board reference designators help identify mounted parts on this GE Mark VI PCB. The board has a number of resistors (R), capacitors (C), and integrated circuits (U).

What do you know about circuit board reference designators?

If you’ve worked with printed circuit boards (PCBs) at all, you’ve noticed the letter codes on their surface. These are called reference designators. If you’ve designed circuit boards, you’ve probably spent more time than you want thinking about them.

What are Reference Designators?

Circuit board letters can be confusing when you first start working with components. These small codes litter the board’s surface and are sometimes hard to read. And sometimes they don’t make sense. Q for transistor? U for integrated circuit? What the heck.

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How To Identify Components on Printed Circuit Boards

Close up view of a printed circuit board
It can be hard to identify all the components on printed circuit boards (PCBs).

If you’ve ever tried to work on your own PCBs, or printed circuit boards, you may have experienced the frustration of looking at a part and not knowing exactly what it is. After working with thousands of PCBs, we understand.

Luckily, there are resources that can help. In fact, lots of them. But they’re scattered all over. And many of the best aren’t even available online anymore unless you know how to use some special tools (Wayback Machine to the rescue!)

But rather than complain about this state of affairs, we decided to create our own tutorial to fix it. Bonus: you benefit, too.

Here’s our printed circuit board component tutorial, with lots of information and pictures to help you identify those individual parts.

Printed Circuit Boards: the Basics

Printed circuit boards are typically made from laminated composite material. This non-conductive substrate sandwiches copper circuitry that actually makes up the circuits the boards are named after.

substrate: /ˈsəbˌstrāt/; an underlying substance or layer.

These copper circuits, also known as signal traces, electrically connect and mechanically support other mounted components on the board.

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