How to ensure good quality PCB assembly
PCB assembly is a method in which a bare PCB will be populated by electronic components through a solder material as a pre-requisite in making a functioning electronic/electrical product. This may be done through automatic electronic component placement or manual / conventional placement depending on the electronic component technology used. In this article, we will be tackling PCB assembly using automatic electronic component placement and how to ensure to produce a good quality PCB assembly output:
1. Solder paste printing
Solder paste printing is the process of placement of solder paste onto the bare PCB using an automatic machine with the aid of a stencil mask. It is a simple process but correct process must be done in order to produce a good output. Insufficient solder volume placement will cause de-wetting defects while too much will produce solder bridging. To ensure this is prevented, solder volume must be controlled through optimizing the printing speed and /or pressure. This is monitored through checking solder paste height. A good practice is to maintain a solder height of 1-3 mils above the actual stencil mask thickness. As an example, if you have a 4 mil stencil mask, maintain a solder paste height output of 5-7 mils.
Solder paste deposit must be sufficient but not too much.
2. Reflow process
Reflow process is the method of heating the PCB populated with electronic components to solidify the solder paste and maintain a permanent electrical connection. If this process is not performed properly, this could cause insufficient solidification of solder paste or worse, electronic component damage. To ensure prevention of these defects or abnormalities, create a reflow profile that is appropriate for the electronic components and solder paste used. A shorter or a longer reflow profile will cause defects and abnormalities therefore, a good practice is to check the solder paste chemistry used (Leaded or Lead free chemistry) and the manufacturer’s datasheets of the electronic components as they provide reflow profile recommendations.
Reflow profile must be in accordance to solder paste chemistry.
These are just some of the PCB assembly processes and its corresponding preventive measures to ensure a good quality output.