0
\$\begingroup\$

enter image description here I am new to reading measurements in datasheet. I am drawing PCB layout of IC LT1761 for my circuit. What I do not understand is what does REF refer to in the datasheet (attached figure)? As far as I understand pin width is 0.62 mm (max) and length is 1.22 mm. Am I correct? Also what is the length of the IC? Is that 2.9 x 1.4 mm?

Thanks you very much for your kind answer.

\$\endgroup\$
  • 1
    \$\begingroup\$ Length of IC? Do you mean L x B of die?Then it is 2.9 X 1.5 mm. You should include Package outline also to avoid overlapping of adjacent components. It is a good practice while PCB design. You can increase pad length also on outer side of pad to ensure proper soldering. \$\endgroup\$ – Electroholic Mar 14 '16 at 7:08
  • \$\begingroup\$ Thanks you for your answer. Another thing I would like to ask is pin base width is 0.62 or 0.45 mm? \$\endgroup\$ – Sui Mar 14 '16 at 7:49
  • 1
    \$\begingroup\$ 0.45 mm is actual part width where as 0.62 mm is recommended width for footprint creation. Normally recommended dimensions are always little greater than actual dimensions for easy soldering. Hope this will help you. \$\endgroup\$ – Electroholic Mar 14 '16 at 8:09
  • 1
    \$\begingroup\$ If you gonna handsolder it, then go for 0.7mm width and 1.4mm length minimum. I would even go for a length of 1.7 mm. Also check the minimum width of the soldermask from your PCB house. It's best to have the wider pin pad but at the same time you need to leave enough space for a soldermask between every 2 adjacent pins. \$\endgroup\$ – GAttuso Mar 14 '16 at 8:45
2
\$\begingroup\$

REF designates a reference dimension and is provided for convenience only. If you look at the drawing carefully, you can work out all the reference dimensions from the main dimensions.

For example, to get the pad height, take the leg span (3.85), subtract the distance between pads (1.4) and divide by two: (3.85-1.4)/2 = 1.225.

You should try to follow the main dimensions when designing a footprint, even though it may not be the most convenient method in the PCB footprint editor.

\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.