Wave Soldering
- Correct orientation of passive components, SOT, SO-IC, QFP, PLCC as regards wave soldering direction
- Allow for "solder thieves" for SMD-ICs
- Don't generally use SMD-ICs with a pitch of < 0.8 for wave soldering
- Allow for minimum distances between neighbouring components in order to prevent bridging. This minimum distance especially depends upon the type of the neighbouring components, their size, the soldering process set-up and its auxiliary agents, and also - to a lesser extent - upon the type of PCB stop mask and among others the age of the areas to be soldered. There are hardly any publications on this special topic. The minimum distances are also often fixed upon other criteria, such as the visual inspectability of the solder joints. From the technical and soldering point of view the limit is at < 1 down to 0.4...0.5mm; but it can vary according to the local conditions on the assembly. Generally it is not advisable to strive for rigid optimization
- Prevention of opens through soldering shadows. The pad protrusions (visible area) must be large enough to prevent shadowing effects
Application Of Solder Paste And Reflow
- Calculate correct amount of solder for sufficient solder fillet
- The dimensions of the footprints should be such as to avoid extensive contact of the non-conductive areas of the SMD with the solder paste
- Solder stop: Provide for studs between the IC pads. Attention: Bridges are a consequence of excessive solder paste application in most of the cases
- Gullwings: Provide for a correct heel fillet by dimensioning the footprints accordingly
- Minimum distances between neighbouring SMDs: From the printing and soldering technique point of view distances down to 0.5 mm are unproblematic. Extremely short distances of 0.2 mm have been realised in the past though