--- In [email protected], "apluscw" <[EMAIL PROTECTED]> wrote:
> > Board density and cost if/when the board goes to production. > Which are not always valid, it is not always true that an SMD is denser than a PTH, especially if layers are limited. On PTH each "pad" is also a "via" and you can route tracks between pins. Routing through dense sets of chips requires a lot of vias in SMD which consume the space freed up by package size. Also, resistors and capacitors do not necessarily have a greater impact on board area. Those decoupling caps you saw on my photo are 0.1" pitch and take up no more surface than an SMD would, and they are coupled to both sides :-) Resistor arrays, of the sort you would use for e.g. pullups take up no more space than SMD. Once I had a board with 16 inputs to comparator circuits that we were doing in SMD. We could not fit the circuit in the space until we switched to resistor networks! True, it was a particlar case because we had a lot of common resistors.....but.... Cost, likewise, needs to be well evaluated. PTH is still used in a lot of high volume production such as consumer goods. Dont put it down to cheap oriental labour costs, more often than not the boards are clearly designed for automatic assembly. The fastest automatic assembly line I have ever seen was for PTH and boy was it fast, firing components like a machine gun. But that was designed for very high volume production and would not be very inefficient on small production runs. On the other hand be careful of making the error that many inexperienced people make regarding hand assembly, that is they assume that the time taken to produce the board is similar to the time they tke to assemble the board on thier workbench. Experienced hand assembly shops are very well organised. Components are cut and bent into bins (usually with a hand crancked machine that eats tape and reeled components) and the boards are then stuffed with the PCBs inserted into frames so that an operator will e.g. stuff say 12 boards at a time. Of course SMD has its good points but remember that there are reasons why there are still so many PTH components around!
