Electronic – what does this number(spacing between pads) in the datasheet mean
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i am going to design footprint for a devise and i need to know spacing between pads. do you know what does (2-1.27) mean?
the devise is pico oem socket.
thanks
Best Answer
1.27 refers to the pad-to-pad pitch. There are 24 pads per column, so 23 intervals. 23 times 1.27 is 29.21 which is shown below. The "2-" refers to the fact that this spacing occurs in two different places, once on the left column and once on the right. It lets you know that the specification does not apply only to the column shown.
Likewise, the specification for the horizontal row small pad spacing "2-1.27(15x)" shows that 16 pads are involved, and the spacing applies both to the upper and lower rows.
It's mostly for self centering purposes. It allows an IC to be misplaced by a small amount and self-correct during reflow.
But this seems to be mainly a NXP only recommendation. They make it for all of their TSSOP parts at least. Their generic SMD footprint and reflow document, AN10365 Surface mount reflow soldering, doesn't address it (directly, unless I glossed over it). But they also reference IPC Standard IPC-7351 Generic requirements for Surface Mount Design and Land Pattern Standard. (You have to pay for standards).
So if you make the outside 5.25mm (more than the minimum), make the pads 1.0 mm, which is 0.111 longer than nominal, you get an inside dimension of 3.25, which is within the allowable range.
Best Answer
1.27 refers to the pad-to-pad pitch. There are 24 pads per column, so 23 intervals. 23 times 1.27 is 29.21 which is shown below. The "2-" refers to the fact that this spacing occurs in two different places, once on the left column and once on the right. It lets you know that the specification does not apply only to the column shown.
Likewise, the specification for the horizontal row small pad spacing "2-1.27(15x)" shows that 16 pads are involved, and the spacing applies both to the upper and lower rows.