Through hole technology
Through hole technology is placed the components on one side of PCB while mount the component lead on the other side of PCB, this drawback of this technology is the large space it will take by components and tremendous drill holes will be required to let the lead of each components through, and normally it won’t be less than 4 leads per component, as a result of that their leads occupy two sides of PCB.
Surface mounted technology
Lead of components will be mounted on the same side as components do, this is call surface mounted device, this kind of technology neither require to mount each lead of component nor need to drill holes for each component’s lead.
Surface mounted technology can even assemble the components on two side of PCB include TOP side and BOTTOM side. Components apply on surface mounted technology also has smaller size compare with those components belongs to through holes technology.
The component density of PCB using surface mounted technology will be higher than the through hole technology PCB. Meanwhile, surface mounted technology component is cheaper than through hole technology component which makes much more populated in the electronic industry.
The downside of surface mounted technology component is the extremely small size which will makes it very difficult to soldering manually. Fortunately over 99% of surface mounted assemble is operated by automatic machine and hand soldering only happen when rework and refurbishment.
PCB assembly manufacturer must know well PCB assembly hole technology and surface mount technology. This process of connecting electronic components to the wires should only be left to experienced companies to avoid fatal mistakes.