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I am designing my very first PCB and there are a few things on the package drawing of my microcontroller that are unclear to me.

enter image description here

  • Why are the sizes expressed in fractions? e.g.: 0,23/0,13 or 0,75/0,45. What does each element stand for
  • What do TYP and SQ stand for?

side question related to the previous one: I am looking for the length of a

enter image description here

is it calculated by: (16,10-12,40)/2 or (15,90-12,40)/2?

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    \$\begingroup\$ TYP = Typical, SQ = Square. The pairs of figures aren't fractions, but maximum/minimum sizes (in mm) \$\endgroup\$ – Brian Drummond Mar 17 '16 at 22:39
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    \$\begingroup\$ Uh, it means square. For example the 16.1mm dimension applies to both the width and length of the chip. \$\endgroup\$ – Brian Drummond Mar 17 '16 at 22:42
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    \$\begingroup\$ The min/max values are there because of mechanical tolerances during manufacturing which the engineers that designed the internals of the IC really have no control over. \$\endgroup\$ – DigitalNinja Mar 17 '16 at 22:51
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    \$\begingroup\$ Somewhere near the page you're on, our should see page with the recommended land pattern, which is what you should use to design your pcb. \$\endgroup\$ – Scott Seidman Mar 17 '16 at 23:27
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    \$\begingroup\$ google.com/url?sa=t&source=web&rct=j&url=http://… page 5 \$\endgroup\$ – Scott Seidman Mar 17 '16 at 23:57
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Summarizing the comments

TYP = Typical, this is used to label a feature that is to be interpreted as exactly the same as nearby comparable features, i.e. the distance between pins are the same in all sides.

SQ = Square, this means the package is square and the four sides have the same size.

Dimensions are given as maximum/minimum in mm.

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