Breaking Down SMT Production

Today, virtually all mass produced electronics feature hardware that has been manufactured with the use of surface mount technology (SMT). These surface mount devices offer numerous benefits over the lead mounted devices that proceeded them, and have completely altered the landscape of the technological sector in terms of what modern electronics are capable of and improved performance. But while most of us in the electronics sector are familiar with SMT production, we may not always take the time to fully appreciate the reasoning behind the development of SMT and what actually goes into the production process. This post will break down SMT, highlighting its industrial significance and the manufacturing process.

Why SMT?

Until quite recently, through-hole technology (leaded devices) were considered to be the best method for mass manufacturing PC boards. Until the electronics industry evolved and adopted SMT production, these leads and the components utilized in the production of through-hole boards put a lot of limitations on what could be done, and made board production more expensive than is actually necessary. Despite the fact that some mechanization was possible, it was necessary that component leads be pre-formed, and in many cases, more components were required. In addition to this, problems often occurred as a result of wires not fitting properly when leads were automatically inserted into boards. This required additional labor and slowed down production rates.

SMT eliminates these issues. It was discovered that the lead wires that hat previously been utilized for connections were not actually necessary in the production of PC boards. Instead of passing leads through holes, the components could be soldered directly onto pads on the board. This made it possible to create more compact and affordable boards, as the drilling of holes was no longer necessary, reduced parts were required, and former problems were resolved. Greater levels of mechanization can be utilized, and the time and costs associated with manufacture is significantly lowered. Although there are certain instances in which through-hole technology must be utilized, the majority of processes associated with PC board production can be improved upon with the use of SMT production.

What components are used for SMT production?

In order to accommodate SMT, a new set of components was required. The components used for surface mount devices are actually quite different from traditional lead components, and can be separated into a few different categories:

• Passive Surface Mount Devices - A wide variety of packages are used for passive surface mount devices, but the majority of these devices are either resistors or capacitors, and package sizes are standardized reasonably well. Resistor and capacitor packages may have size designations of 1812, 1206, 0805, 0603, 0402, or 0201. Coils, crystals, and other components will generally have more specific, individual requirements. Connections to the PCB are made via metallic areas at either end of the package. 

• Transistors and Diodes - You'll typically find these components within small plastic packages, with the connections being made through leads emanating from the package. They are bent so they contact the board. Three leads are always utilized for these packages so that it's easier to identify which way around the device needs to go.

• Integrated Circuits - Multiple packages are available for integrated circuits, depending on the level of interconnectivity that is necessary. Simple logic chips, for instance, may only require 14 or 16 pins while others such as VLSI processors and associated chips may need upwards of 200. In addition to standardized packages for smaller chips and VLSI chips, there are also other packages such as a ball grid array (BGA). Here, the connections are underneath the package as opposed to on the side. The connection pads contain balls of solder that melt throughout the soldering process which allows for a good connection with the board. Since the entire underside of the package can be utilized, the pitch of the connections is wider and is generally believed to be more reliable.