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AD9650 Land Pattern

Question asked by MartinISDC on Jun 11, 2014
Latest reply on Jun 17, 2014 by Anthony.DeSimone

Hello All,

 

I had a few questions with the landing pattern of the AD9650. Since the datasheet for the AD9650 did not directly reference a desired land pattern for the PCB, I looked at the application note AN-772 to determine the required dimensions.

 

I'll list the constants I used to determine the pad length. I used the AD9650 datasheet and the generic dimensions for the 64 LFCSP package.

 

Dmin - 8.9 mm

Jt - .1 mm

Tt - .31 mm


Lead Pitch - .5 mm

# of leads on side - 1 = 16 - 1 = 15

Pad Width - .28mm (from look up table assuming .5 mm pitch)

CLL - .22 mm (was not explicitly defined on data sheet or package information, but .22 mm minimum would satisfy the requirements defiend in the App Note)

 

Using ZDMax = Dmin + 2Jt + Tt, ZDMax = 9.41mm

 

GDmin >= ADmax + 2*CLL, GD >= (Lead Pitch * No of Leads on Side - 1) + pad width + 2 * CLL >= .5 * 15 + .28 + 2*.22 =8.22 mm

 

Since the AD9650 has a .5 mm pitch, the X (width) of the pad length would be .28 mm.

And Y = (ZDMax - GDMin) / 2 = (9.41 mm - 8.22 mm)/2 = .595 mm.

 

These seemed like reasonable numbers, but I wanted to cross reference Analog's own footprint found here: ad9650 | Symbols and Footprints | Analog Device

 

just as a double check. I used the Ultra Librarian software to open the file and converted it to a library file for EAGLE PCB. The results differed significantly to the values I had calculated. The pad length was set at .3048 x .8128 instead of the calculated (.28 x .595 mm) [which would have satisfied the pad tolerance of the AD9650]. What was also strange was that the exposed pad dimensions were set to 7.64 mm x 7.64 mm (which exceeds the maximum dimensions of the exposed pad by almost a .1 mm per side) instead of the nominal 7.5 mm x 7.5 mm.

 

Before continuing with the board layout, I wanted to confirm that the package for the AD9650 that was provided by Analog Devices was correctly defined. And I wanted to know how to calculate the correct values for pad length, position, etc.


Thanks for all the help.

 

-Martin

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