Inductor footprint is too big for the inductor that will be placed on it.

[treez]

Hello,
We have got our PCB layed out with the wurth 768775256 SMD inductor…

wurth 768775256 SMD inductor:
https://katalog.we-online.de/pbs/datasheet/768775256.pdf

This is too expensive, and instead, we wish to place the following smaller inductor on its footprint…
(SDR0503-471KL):
https://www.farnell.com/datasheets/...1.1152887236.1502255272-1679746183.1489787856

will this be OK, or will the smaller part slide about and misalign on the too-big pads?
(Its use is in a CLC filter upstream of a 1W buck converter)

 

[smijesh]

Big pad size is not an issue in pick and place machine or hand soldering, it is actually good, solder will flow properly hence good mechanical and electrical bounding between part and the pad (Pad to pad distance is less(0.1mm) in bourns parts but it is ok in normal voltage(<400V) application). It will pass IPC 610 standard

 

[SLK001]

The smaller part has much higher resistance (5.70 vs 1.77Ω), so the Q will be lower. Depending of the filter requirements, the small part may not work for you. If the requirements are still met with the smaller L, then the footprint of the bigger one will be okay to use for the smaller one.

 

[FvM]

Higher voltage drop of the DC filter is the main difference, I presume treez is aware of it.

 

[treez]

the footprint of the bigger one will be okay to use for the smaller one

Thanks, may i ask about the following alternative even smaller inductor on the above footprint?......this one has a gap between its pads of just 1.4mm, whereas the footprint it is to sit on has 2mm between the pads.....so in other words, some of the smaller inductors metal pad will be sat on solder resist. Will this be OK?

744045471 Inductor
https://katalog.we-online.com/pbs/datasheet/744045471.pdf

 

[SLK001]

Will this be OK?

It should be okay. If one side hits liquidus first, it looks like there is still enough of the part on the second pad to pull it back to the correct position on the pad. There is a possibility that the part could be lifted above the second pad if one side hits liquidus first, so run the smaller part by one of your production engineers.

This smaller part is really stretching the limit of being able to fit on the pad for a production environment. If things were hand soldered, I wouldn't have much of a concern, but using reflow soldering, the forces on the part could be enough to really screw things up. Your production engineer might just say "no" to the smaller part due to these concerns. If so, it's board redesign time.

Are you getting push-back from the bean counters with your first part? If so, present them with the cost of a new board design, the cost of scraping the boards and the time lost for procurring new boards. They will go with the first part every time.