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ESP32 Optoisolated Programmer – PCB Analysis #1

Welcome to the continuation of our mini-series of blogs about the ESP32 Optoisolated Programmer – PCB Analysis #1. Enjoy!

The cost of manufacturing electronic devices depends largely on the design of the device itself. Everything can be designed, but not everything can be manufactured easily and quickly. Design errors can result in unnecessary tasks being performed throughout the production process, which senselessly increases the cost of the device without adding any value to the end customer.

SMD and THT component layout

The assembly process of electronic devices consists of many stages. We are more interested in SMT assembly (surface-mounted elements) and THT assembly (soldering of elements).

The first step when designing a PCB is to consider whether the SMD components will be placed on one or both sides of the PCB. It also has a big influence on the mounting of the THT elements. 

It would be ideal to choose all the components so that they are all SMD only and there are no through-hole components. However, such a luxury is rarely possible, and the use of through-hole components is a must. Soldering of through-hole components is easiest when they are all located on one side of the board and there is nothing on the other side. Then all components are placed on the top side and all simultaneously are soldered on the bottom side using a flat wave, looking like a fountain of liquid tin, which pours the board from underneath and solders all components simultaneously.

It is advantageous to have all the SMD components on the same side as the through-hole components. This way, in the manufacturing process, we populate all SMD components simultaneously and solder them on the same assembly line. 

However, if the board size is as small as possible, and the price is less important, we can consider the double-sided assembly of SMD components. Then, we have to reckon with doubling the cost of SMD assembly, because the board must go through the assembly line twice. 

In addition, the presence of SMD components on both sides makes it impossible to solder THT components on a plane wave, because the SMD elements on the bottom side would be desoldered and washed away by the wave. The solution to this problem is to glue the SMD components, but this is a more expensive process than standard soldering them with solder paste. Another option is to use selective wave, which solders only selected areas of the board, avoiding SMD elements, but this solution is also expensive. Another option, rather possible only for small production runs, is hand soldering.

Bearing in mind all the above considerations, we decided that our programmer will have SMD and THT components on the top side. This arrangement will allow for maximum production cost reduction.

 

Stay tuned for more information about our PCB Analysis. Until the next time!

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