What is SMT?

 

The Advantages of SMT

The main advantages of SMT over the older through-hole technique are:

Smaller components. As of 2012 smallest was 0.4 × 0.2 mm (0.016 in × 0.008 in: 01005).

Much higher component density (components per unit area) and many more connections per component.

Lower initial cost and time of setting up for production.

Fewer holes need to be drilled.

Simpler and faster automated assembly. Some placement machines are capable of placing more than 136,000 components per hour.

Small errors in component placement are corrected automatically as the surface tension of molten solder pulls components into alignment with solder pads.

Components can be placed on both sides of the circuit board.

Lower resistance and inductance at the connection; consequently, fewer unwanted RF signal effects and better and more predictable high-frequency performance.

Better mechanical performance under shake and vibration conditions.

Many SMT parts cost less than equivalent through-hole parts.

Better EMC compatibility (lower radiated emissions) due to the smaller radiation loop area (because of the smaller package) and the smaller lead inductance?
 

The Disadvantages of SMT

Manual prototype assembly or component-level repair is more difficult and requires skilled operators and more expensive tools, due to the small sizes and lead spacings of many SMDs.

SMDs cannot be used directly with plug-in breadboards (a quick snap-and-play prototyping tool), requiring either a custom PCB for every prototype or the mounting of the SMD upon a pin-leaded carrier. For prototyping around a specific SMD component, a less-expensive breakout board may be used. Additionally, strip board style protoboards can be used, some of which include pads for standard sized

SMD comportments. For prototyping, “dead bug” breadboarding can be used.

SMDs’ solder connections may be damaged by potting compounds going through thermal cycling.

Solder joint dimensions in SMT quickly become much smaller as advances are made toward ultra-fine pitch technology. The reliability of solder joints become more of a concern, as less and less solder is allowed for each joint. Voiding is a fault commonly associated with solder joints, especially when reflowing a solder paste in the SMT application. The presence of voids can deteriorate the joint strength and eventually lead to joint failure.

SMT is unsuitable for large, high-power, or high-voltage parts, for example in power circuitry. It is common to combine SMT and through-hole construction, with transformers, heat-sinked power semiconductors, physically large capacitors, fuses, connectors, and so on mounted on one side of the PCB through holes.

SMT is unsuitable as the sole attachment method for components that are subject to frequent mechanical stress, such as connectors that are used to interface with external devices that are frequently attached and detached.

Although it is possible to use some SMT components for home construction, great care is required when soldering them. Additionally even the ICs having a wide pin spacing may be difficult to solder. Those with fifty or more pins cannot be soldered without special equipment. They are intended only for large scale manufacturing. Even when working on boards that have already been built great care is needed. However these SMT components offer great cost savings to manufacturers and this is why they have been adopted. Fortunately for the home constructor, traditional leaded components that can be soldered manually are still widely available and offer a much better solution for home construction. Nevertheless SMT components can be used for some home projects where they are applicable – where the SMT component leads and connections are not too small to manage with more traditional soldering irons and other tools.

SMT is used almost exclusively for the manufacture of electronic circuit boards these days. They are smaller, often offer a better level of performance and they can be used with automated pick and place machine that in many cases all bit eliminate the need for manual intervention in the assembly process.

Wired components were always difficult to place automatically because the wires needed to be pre-formed to fit the relevant hole spacing, and even then they were prone to problems with placement.

Although many connectors and some other components still require assisted placement, printed circuit boards are normally developed to reduce this to an absolute minimum, even to the extent of altering the design to use components that can be placed automatically. In addition to this, component manufacturers have developed some specialised surface mount versions of components that enable virtually complete automated assembly for most boards.

SMT (surface mount technology) component placement systems, commonly called pick-and-place machines or P&Ps, are robotic machines which are used to place surface-mount devices (SMDs) onto a printed circuit board (PCB). They are used for high speed, high precision placing of broad range of electronic components, like capacitors, resistors, integrated circuits onto the PCBs which are in turn used in computers, consumer electronics as well as industrial, medical, automotive, military and telecommunications equipment.