Why does this multi-resistor package have curved pads?

[treez]

Hello
On the final page of this multi-resistor datasheet, it shows the land patterns for the "CAT16-F4" resistors package and the "CAY16-F4" resistors package.

What is the reason for having these two different land patterns for what are essentially the same package of resistors?
Why does the "CAT16-F4" package have curved pads?….why would they bother to manufacture curved pads when straight, square pads are fine?

Also, on the final page, there is text labelling the land patterns, and in one place the text reads "Land"......what does this mean?......(I know what a copper "land" is but the diagram appears to be pointing to a connecting trace and calling it a "land"...why is this?)


SMD multi resistor datasheet...
https://www.farnell.com/datasheets/698458.pdf

 

[dick_freebird]

These "castellated" pads are typical of certain LCC package
styles. I believe the form is useful to obtain a good solder
fillet while not extending the package footprint significantly.
A flat pad would put some solder proud of the ceramic body.

 

[treez]

thanks, but then why do some of them have flat pads?, why don't they all have castellated pads?....eg the CAY16-F4

 

[dick_freebird]

Maybe just because somebody asked for it. Often I've had
more than one option in front of me, and just went with
whatever the customer said they preferred. Which may have
a rational basis, or not. The next guy might want something
different, but if they don't want to pay for test fixturing,
qualifying the second package and so on, they can just learn
to like what's on the shelf at that point.

There's often a little sliver of time where "why?" matters.
Then it's a done deal and you get on with life.

Within the same edge-extent, the castellated pin does give
you about 55% more wetted area. The fillet is also inspectable
because it is aside, not under, the package body (this is a
big deal in some end markets). But there seems to be no great
love for the style, generally; you lose any lead compliance
that would pick you up some ability to tolerate packageCB
TCE mismatch and so on, placing the solder joint under more
strain and rate / risk of failure even if it's prettier and more
inspectable to begin with.

www.rfm.com/products/apnotes/pcb_web.pdf

 

[FvM]

Referring to your original question, the land patterns are not different, except for a sligthly different suggested length range. So both types fit well the same PCB footprint.

Everything else is matter of taste. Personally I prefer the concave type fro protyping. Production type at assembly house's conevience.