0
\$\begingroup\$

We are working on a design that uses the Analog Devices HMC321A. The datasheet does not specify a recommended footprint; they do specify the IC dimensions. The pins/pads on the chip have a nominal 0.25mm width. This suggests that the footprint pads should be 0.25mm. The maximum width is specified to be 0.3mm.

We are considering making the pads of the footprint 0.3mm (the main reason being that the traces are 0.3mm wide — calculated so that we achieve the target 50Ω impedance; with 0.3mm pads, we don't need any tapering from the trace to the IC's pad).

Any comments on whether this is a good idea? In particular, I'm worried about two aspects:

  • Will this cause manufacturability issues? (soldering a 0.25mm pin to a pad wider than intended)
  • Will it degrade the matching at the connection from the IC's pin to the PCB's pad? (since the RF engineers that designed that IC would have perhaps calculated/simulated everything under the assumption of soldering that pin to a 0.25mm pad?)
\$\endgroup\$
2
  • 1
    \$\begingroup\$ did you check the EV1HMC321ALP4E as well? What is your intended frequency range? \$\endgroup\$ Feb 3 at 18:51
  • 1
    \$\begingroup\$ It's generally correct practice to make the pads wider than the pins, to help self-centering during reflow. \$\endgroup\$
    – TimWescott
    Feb 3 at 21:03

1 Answer 1

0
\$\begingroup\$

Analog Devices product webpage references under the "Design Resources" section the following link to an ultralibarian entry including a symbol, a footprint, and a 3D model: https://vendor.ultralibrarian.com/adi/embedded?vdrPN=HMC321ALP4E

There is another link to an evaluation board too, which can be used as reference.

It is not uncommon to make the landing pads bigger than the pin itself, i.e. as big as the maximum pad width. If I am not mistaken the footprint provided by ultralibarian has 0.3 mm pads.

Regarding matching, I would assume that the IC engineers assume that the board engineers will take care of this. I.e. typically matching is done during prototyping because of its sensitivity to geometry, which is highly influenced by production processes; even the amount of solder or component size used can have significant influence. Of course, this highly depends on the frequency range you are planing to use. Note: AD provide s-parameters on their website as well, if you want to setup a "full PCB" simulation.

\$\endgroup\$
2
  • \$\begingroup\$ No, they all (there are three footprints; without any suffix, suffix M, and suffix L — no idea why, or what each of those is supposed to represent) have 0.25mm pads (more precisely, 0.01" pads, or 0.254mm) \$\endgroup\$
    – Cal-linux
    Feb 3 at 21:17
  • \$\begingroup\$ indeed. it looked to me like that in the online viewer tool. \$\endgroup\$ Feb 4 at 10:25

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

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