Understanding Surface Mount PCB And Its Assembly

 
Printed circuits boards designed to be fitted with surface mount components are ubiquitous today. Surface mount PCB is present in most of today’s electronic devices. Compared to its predecessors, surface mount PCB provides more benefits in term of performance and manufacturability. Surface mount technology wasn’t widely used until the 1980s. However, the story is very different today as nearly all-electronic hardware is manufactured using surface mount technology.

Essential to PCB assembly and design, surface mount technology has improved the overall performance and quality of PCBs. Furthermore, it has greatly reduced the costs of handling and processing. Unlike through-hole, surface mount PCB does not require holes to be drilled through a printed circuit board. Furthermore, the components of surface mount are smaller and can be mounted on both sides of the board. This technology ensures smaller, high performing and much denser PCBs due to its ability to fit many small components on a PCB.

There are many benefits of using surface mount including:
• More space to work with and higher component density
• Is stable and performs extremely well in vibration and shake conditions
• Allows smaller PCB size
• Compared to through techniques, provides a much more reliable and repeatable solder joint formation
• Ensures faster production time and lower cost
• Compared to a thousand for through hole manufacturing, SMT components can be placed during PCB assembly at rates of thousands and sometimes tens of thousands of placements per hour

Assembling surface mount pads is a complex process. In order to make sure the screen stencil and surface of the PCB under print engage perfectly, the pads must be flat. A gap will develop if any dabs are present on the pads. This in turn will cause the solder paste to spill out. You will experience PCB assembly failure if the printing is solder pasted poorly because poor solder pasting of the printing can lead to solder balls and short circuits. Therefore, surface mounts pads must lay perfectly flat on PCBs.

Achieving a reasonably flat pad as well as controlling it is difficult with traditional techniques such as Hot Air Solder Leveling (HASL). Furthermore, the risk to warping PCB panels is ever-present due to the extreme temperatures of the machines involved.. However, this is something you won’t experience with a surface-mounted pad as its copper finish is adequately flat.

An anti-tarnish finish that avoids damage and remnants staying on the test probes, permits electrical contact with probes, and takes solder is required for assembling surface mount pads. Flux varnishes and solderable preservatives are cheap solutions. However, they allow the copper pads of the PCBs to retain the color and figuring out whether the entire circuit board surface has been tended is difficult. Furthermore, durability and shelf life are limited. The solution here is the immersion silver (IS) process. The process provides solderability and an elongated life.

Furthermore, it causes little stress to the panels of the printed circuit board and is cost effective. There is no risk of panels being warped and PCBs flat extremely flat surface mount pads. Finally, it ensures the long-term reliability of the circuits.