Reason for shifting two places past the decimal point in IPC Naming?

Hello,

There is a rule in IPC 7351-B, footprint naming convention where we need to shift 2 decimal places right for Body width/Lead Span/Pitch and similarly one place for chip packages.
(Example OSCCC6.7X4.2X1.5 to OSCCC670X420X150 and RESC3.4 0.8X0.6 to RESC3408X60)

Notes as per IPC naming document,
• All dimensions are in Metric Units
• All Lead Span and Height numbers go two places past the decimal point and “include” trailing Zeros
• All Lead Span and Body Sizes go two place before the decimal point and “remove” leading Zeros
• All Chip Component Body Sizes are one place to each side of the decimal point
• Pitch Values are two places to the right & left of decimal point with no leading Zeros but include trailing zeros

Do there any valid reason why the rule is recommended:?: Just to follow legible naming:?: Anyone pl help!!

Thanks,
Manuj

You may be able to get a better answer to this from the team on pcblibraries.com forum as They had a great deal of input into the naming convention.

It's probably to cater for the very fine pitch components that we are seeing now where they do go to 2 decimal places and so as a format it needs to incorporate this even for the not so fine components as a calculator program will use these values.
Ask Tom Hausherr and I'm sure he can explain, I don't think he is a member of here.

Hi Matty,

Thanks for the info. I posted in Pcblibraries forum.
www.pcblibraries.com/forum/shifting-ahead-two-decimal-points-in-ipc-naming_topic2030.html

Manuj