Miniaturization has always been on top of the list as the electronic industry has progressed. Now with miniaturization technology in hand, it has become possible to make components and devices, which costs less and run efficiently. Surface mount technology is one such significant contributor, which has helped miniaturization to move one step ahead.
Surface mount technology (SMT) is state-of-the-art construction method for assembling printed circuit boards with components soldered to the surface rather than to plate through-holes.
The main advantages of SMT over through-hole technology are:
1. Both sides of a circuit board can be used (which helps to reduce the size of an assembly).
2. It becomes easier to design and make multi-layer circuit boards, therefore leading to a decrease in size.
3. Surface mount lends itself to automated assembly and therefore, when used for volume production, it can offer lower costs.
4. Smaller components can be used, allowing increased circuit density.
In addition, Surface mounting can also be used for high degree of automation, reducing labour cost and greatly increasing production rates. SMDs can be one-quarter to one-tenth the size and weight, and one-half to one-quarter the cost of through-hole parts.
Depending on how the components are distributed, the assemblies can be of three types:
1. Type-1 assembly: SMDs on both sides
2. Type-2 assembly : SMDs on one side and insertion-mount components (IMCs) on the other side
3. Type-3 assembly: Randomly distributed SMDs and IMCs on either side
Out of these three, type-3 assembly is the better choice as far as ease of `designing` is concerned but difficult from the manufacturing point of view.
In the first stage of standard surface mount process, using a stainless stencil that matches the component pattern, solder paste (a sticky mixture of flux and tiny solder particles) is applied on the surface of the circuit board. After this stage, the components are then kept on the printed paste. They first enter a pre-heat zone, where the temperature of the board and all the components is gradually, uniformly raised. This helps minimize thermal stresses when the assemblies cool down after soldering. Following this, the boards enter a zone where the temperature is high enough to melt the solder particles in the solder paste, bonding the component leads to the pads on the circuit board. The surface tension of the molten solder helps keep the components in place, and if the solder pad geometries are correctly designed, surface tension automatically aligns the components on their pads.
As the board moves down the production line, the paste keeps the components in place. Thus after placing all the components in respective places, the assembly is made to pass through a re-flow oven, where melting of the solder takes place to form the joints. As soon as it comes out of the oven, that part of the assembly is then complete. The board may then be packaged or possibly the second side assembled.
Though SMDs are a boon for certain segments, they are still cost-intensive. Many industries still and will continue to use lower-cost THT with effective results. In addition, there are also some disadvantages related to SMD such as slight overheating problem, visual inspection difficulty and more importantly they are harder to hand assemble.
But at the same time, there is lot of pressure to reduce the size and increase the functionality of gadgets. And, this can only be achieved using SMT technology, as it is becoming one of the basic needs today. To be precise, consumer preference to go for good quality and less costlier products has driven SMD industry towards manufacturing thinner component with higher number of inputs/outputs per package. Hence, to cater the increased number and functionality of electronic systems, the near future will invest lot on SMD technology.