Trouble reading a variable inductor (tunable RF coil) datasheet

Question

I have a trouble reading this datasheet for the Coilcraft 7mm Tunable RF Coils – 146, 150 Series. I see there are two main types of such inductor: with shield can and without it. I'm going to buy one without it.

This picture is what bothers me. On the upper right picture you see those small circles with 'start' and 'finish' notes, which present the pins.

• First question is a very basic one. When you look at Recommended Board Layout, why are these pins mirrored? My assumption is that's because this board layout is meant to present the footprint of an opposite side of the PCB, so one side of it is where elements are, the other side is where connections most of the times are, and so when planning connections I should use this mirrored layout, and that's why it's here. Am I correct?

• The second question is about those larger holes on the board layout. It says that the left one is "for shield can tabs", but for the second one it doesn't say anything. So when using unshielded styles, can both of those large holes be ignored, or only the left one?

Answer 1

Usually these days we lay out boards as if we were looking down through the board from the component side.

Many years ago, with single-sided boards, it was not uncommon to lay out boards using sticky donuts and tape looking at the copper side, but that's not really the way it's done today.

As far as the the shield tab holes go- it's not uncommon to only label one feature on a mechanical drawing when there are obvious symmetrical features that are the same size. Sometimes the number is specified (eg. 2pl), sometimes not. So you don't need either of the holes if there is no shield. Note the description is plural.

Of course if you like to avoid issues, it's always best to have a sample of the part in your hand as a double check.

Answer 2

Coil choices are a trade-off of leakage or Q and self resonant frequency\

Shielded offer lower leakage to crosstalk but lower the self-resonant frequency (SRF) or Q by about 20%.

Your specs are the most important part for any design.

**The layout shows the drill patterns for the COMPONENT side of the shielded part only. The bottom view to the left shows the tuning slot is accessible to both sides, which means an extra hole may added to the pattern if service or tuning is desirable from the solder side.

The unshielded top/bottom view orientation makes no difference, so the layout is not shown for that part with the 2 smaller holes.

The reason wave-solder ONLY is specified is the thermal transfer problem with soldering this thru-hole part, so the view is SOLDER SIDE is shown, contrary to what others have said. Naturally, hand-soldering like-wise is done from the solder side and pad size is not critical and not specified. Only the finished hole size is critical for placement.

(apologies for my dyslexic Murphy's Law with original answer)

Also plan on having a plastic screw driver that fits to avoid the magnetic effects and duress that can crack brittle ferrite with a sharp metal edge.