Author Topic: PCB footprint for WQFN-16  (Read 1282 times)

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Offline OM222OTopic starter

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PCB footprint for WQFN-16
« on: October 06, 2019, 12:05:52 pm »
I wanted to design a footprint for the QFN version of the ADS1219, but I'm not sure which dimensions to use. The default packages in my design tool use 1.6mm squared for the thermal pad, but the T.I. datasheet specifies half of that, with only 0.8mm squared! (page42)
http://www.ti.com/lit/ds/symlink/ads1219.pdf?HQS=TI-null-null-mousermode-df-pf-null-wwe&DCM=yes

this leaves a large gap between the thermal pad and the rest of the pads which is nice since it prevents shorts by solder bridges, but it also seems too small, I could only fit 1 via inside that pad with minimum hole size that manufacturers recommend (10 mills). from the images I can also see the exposed pad goes a lot closer to the rest of pads (more inline with the 1.6mm squared) , so I'm not sure which dimensions to use.
« Last Edit: October 06, 2019, 12:13:37 pm by OM222O »
 

Offline ThomasDK

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Re: PCB footprint for WQFN-16
« Reply #1 on: October 06, 2019, 02:16:26 pm »
The ADC uses less than 0.5mA, so I wouldn't worry about thermal vias.

I would do as TI recommends - the datasheet even shows the single via in the pad.
 

Online wraper

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Re: PCB footprint for WQFN-16
« Reply #2 on: October 06, 2019, 02:34:12 pm »
You can make it equal to pad dimensions on IC but make sure to reduce aperture of solder paste stencil to about 50% of area of the pad itself.
 

Online wraper

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Re: PCB footprint for WQFN-16
« Reply #3 on: October 06, 2019, 02:39:14 pm »
Pages 41 and 42 of the datasheet show packages with contradictory thermal pad size. Second one matching that footprint with tiny pad. IMHO look on actual IC and make accordingly.
EDIT: but picture on page 41 with larger pad does not have pad dimensions. So most likely this IC just has such tiny thermal pad.
« Last Edit: October 06, 2019, 02:44:41 pm by wraper »
 

Offline isometrik

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Re: PCB footprint for WQFN-16
« Reply #4 on: October 06, 2019, 02:59:04 pm »
Page 43 of the datasheet shows the recommended footprint (land pattern data).
 

Offline OM222OTopic starter

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Re: PCB footprint for WQFN-16
« Reply #5 on: October 06, 2019, 06:20:55 pm »
I think will stick to the pad size specified by the datasheet, since like Thomas mentioned, I don't think the thermal via isn't even necessary in those power levels. It just seemed a bit odd to me.
 


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