SMD Soldering Guide
This guide is meant to help in the soldering of SMD components on PCBs. A single board could be composed of two side, with only one being SMD. This guide is not meant to help in the soldering of boards with SMD components on both sides, as for such processes a soldering oven is needed. PDF
Before Soldering
Solder paste prepping
There are multiple guidelines to use when selecting the proper solder paste, but they are not the focus of these guide.
Once a solder paste is selected it is advisable to keep it refrigerated, as per datasheet recommendation.
Before starting the soldering process, allow the solder paste to reach room temperature if it has been stored in a refrigerator. Then, vigorously mix the solder paste for a few minutes. This ensures proper distribution of the flux and improves its spreadability during application. The paste should be uniform and easily malleable to pass effectively through the stencil.
If the paste appears excessively dry due to improper storage, it is possible, as a last resort, to re-plasticize the flux resin by adding a few drops of a specific solvent (e.g., ROL0 resin with a 70% ethanol, 30% white spirit solution). This should be considered a temporary fix while waiting to obtain fresh solder paste.
Board and stencil prepping
It is advisable to clean both the board and the stencil with isopropil alchool (>90°). to remove any contaminants. This step is essential to ensure a clean and durable solder joint.
Stencil pre-heating
Insert the PCB into the adapter to align it with the stencil. Evenly preheat the PCB and stencil using a hot air station (approx. 100°C). Be careful not to deform the stencil with excessive heat.
Stencil application
Apply the solder paste in two or three spots along the long side of the board. Use a spatula to spread it parallel to the short side, moving left to right and vice versa.
Visually inspect the application: the paste should be confined within the pads, without connecting them. Repeat if necessary.
Esempio di Applicazione errata:
Correzione:
Esempi di applicazione corretta:
Component placement
Using SMD tweezers and a KiCad plugin (HTML Bom) , place the components following the positions and quantities specified in the BOM. Mark off the components as you place them to avoid mistakes.
