QFN package to add: 20pin 3x3mm Pitch0.4mm

I’m hoping @maui may help: I came across a package for the ATTiny 816 not covered by the 3d model set. I hope I have done a reasonable parameter set for it here:

'QFN-20-1EP_3x3mm_Pitch0.4mm': Params( # from Microchip ATtiny816, claims JEDEC MO-220 var VEEE
		c = 0.2,        # pin thickness, body center part height
#   K=0.2,          # Fillet radius for pin edges
		L = 0.4,        # pin top flat part length (including fillet radius)
		fp_s = True,     # True for circular pinmark, False for square pinmark (useful for diodes)
		fp_r = 0.5,     # first pin indicator radius
		fp_d = 0.1,     # first pin indicator distance from edge
		fp_z = 0.01,     # first pin indicator depth
		ef = 0.0, # 0.05, # fillet of edges  Note: bigger bytes model with fillet
		cce = 0.2,      #0.45 chamfer of the epad 1st pin corner
		D = 3.0,       # body overall length
		E = 3.0,       # body overall width
		A1 = 0.035,  # body-board separation  maui to check
		A2 = 0.90,  # body height (var 0.8 .. 0.9)
		b = 0.2,  # pin width
		e = 0.4,  # pin (center-to-center) distance
		m = 0.0,  # margin between pins and body  
		ps = 'rounded',   # rounded pads
		npx = 5,  # number of pins along X axis (width)
		npy = 5,  # number of pins along y axis (length)
		epad = (1.7, 1.7), # e Pad #epad = None, # e Pad
		excluded_pins = None, #no pin excluded
		modelName = 'QFN-20-1EP_3x3mm_Pitch0.4mm', #modelName
		rotation = -90, # rotation if required
		dest_dir_prefix = '../Housings_DFN_QFN.3dshapes/'
		),

The package is no smaller than the QFN-24 3x3; there are just fewer pins.

I used as my starting point the existing “QFN-20_3x3mm_Pitch0.4mm”, and in addition to the number of pins (6 -> 5) have changed A1, A2 to match the microchip package, and added the epad there is a 1.7mm square pad with a chamfer). Does this mean we need alternate packages for 24pin too or are the changes insignificant?

I couldn’t see a way in the params to represent the chamfered corners of all 8 corner pins on the underside; not sure if we care about that or not. In addition, I think ‘ps’ should probably be rectangular, or similar: the drawing shows sharp pad corners.

The datasheet I worked from is http://ww1.microchip.com/downloads/en/DeviceDoc/40001901A.pdf, page 466.

Hope this helps.

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Is there currently a footprint for this in the official library? And for a chamfered corner you can set the parameter “cce”

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Hi @rivimey
nice to see you working with the scripts :smiley:

For this package what you have done is already good!
Normally for 3D mechanical conversion the main body size is what is needed… pads are also useful to have a nice representation of the chip and also to check the footprint…


Chamfering also the external pins can be done, but it is little relevant for the pcb and also for the mechanical conversion…
For that reason the scripts are not considering these cases…
Inside the script there is already a chip with similar dimensions, apart the height which is smaller…
UQFN-20-1EP_3x3mm_Pitch0.4mm
the reference is here

Nice to see new guys working with the 3D mechanical library :smiley:
Maurice

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@maui, Thanks for that.
@shack
I didn’t look very hard for the footprint, to be fair. I didn’t see the UQFN-20 because… U:slight_smile:
I believe the ‘cce’ parameter is for the exposed pad, but I was referring to the 8 signal pads that are chamfered as well.
Regards,
Ruth