Some packages are problematic. They can have a pitch of for example either 0.6mm, 0.65mm, or maybe even 0.635mm (referenced to some banana unit). Such differences are too small to see, but when you have a 16 pin IC package, the difference is just big enough to cause a problem.
Similar with the Green / industrial terminal blocks. They are sold both in 5mm pitch and in 5.08mm pitch. For two or 3 pole blocks they are exchangeable, but for a 16 pole connector, the differences accumulate and it won't fit anymore.
But when the package pitch is the same. It really does not matter much. An old (Dos age) program I had long ago had different libraries for "technology class". Some libraries had big pads and are easy to solder. Other library sets had smaller pads for the same IC's. Those need more accurate SMT placement, but the PCB can be made denser.
When Solder melts, it flows around any area it can wet, and it will it's shape according to surface tension, so a lot of variability can be tolerated. But there are a bunch of factors that are critical to keep within range. For example either too much or too little solder paste will result in unreliable PCB's. And guess what. Some PCB / Stencil manufacturers make the stencil apertures as you created them, other stencil manufacturers shrink all apertures by some (arbitrary?) amount. This inserts a lot of uncertainty in what should be simple. Solder stencils also come in different thicknesses, and this also changes the amount of paste for each pad.
So as long as the pitch is right, and pad size and location sort of looks OK, it is very likely good enough, but there are more factors that can dominate.
Home
Help
Search
Login
Register
