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IPC-7351B Land Pattern Naming Convention Flaws

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Tom H View Drop Down
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    Posted: 07 May 2018 at 12:35pm
In the 2010 release of IPC-7351B the Land Pattern Naming Convention produces duplicate names. 

These are the some of the issues that need you need to be careful of. 

The first thing that PCB Libraries did was to rearrange the land pattern name to make every component package have symmetry to the name. The BGA had the Pin Qty at the beginning of the land pattern name. The QFP had the Pin Qty at the end of the land pattern name. Every PTH land pattern had the Pin Qty at the beginning of the land pattern name. 

To fix this issue and make all land pattern names, we put all the Pin Qty. at the beginning of the land pattern name. The Component Family Prefix is 1st and the Pin Qty. is 2nd. 

Gull Wing leaded parts. The naming convention does not include the Nominal Terminal Lead Length and Width and this directly affects the pad length. If all the component dimensions were the same, but the Nominal Terminal Lead Length and Width was different, the IPC Calculator would produce the same land pattern name if the Nominal Terminal Lead was between 0.20 - 0.80 - QFP144P50_2200X2200X120
however, the pad sizes would be different for each Terminal Lead Length and Width. 

To fix this issue, PCB Libraries added the Nominal Terminal Lead Length X Width to the Land Pattern Name - QFP144P50_2200X2200X120L60X22

Another issue are Thermal Tab Sizes for SON, QFN, PSON, PQFN, SOP, QFP, etc. All the component dimensions could be identical for a 24 pin QFN but the Thermal Tab could have dozens of different dimensions and square or rectangle shapes. The IPC Calculator would produce a duplicate land pattern name for every 24 pin QFN regardless of the Thermal Tab size. 

To fix this issue, PCB Libraries added the Thermal Tab Length X Width to the Land Pattern Name -QFN25P40_400X300X80L40X20T265X165

However, if the Thermal Tab shape is Square, then the land pattern name would be - 
QFN25P40_400X300X80L40X20T265

Another issue is the BGA component family. If all the BGA dimensions are the same except the Baal Diameter ranges from 0.30 - 0.50 the IPC Calculator would produce a duplicate land pattern name for every BGA even though the Pad Size would be different. 

To fix this issue, PCB Libraries added the Ball Size to the Land Pattern Name - 
BGA49CP80_7X7_700X700X155B50

Another issue is the SOIC and SOP component family. IPC-7351B land pattern name does not include the Body Length. You can have a SOIC where every dimension is identical except the Nominal Body Length is different. This affects the silkscreen Legend, Assembly and Courtyard Outlines. 

To fix this issue, PCB Libraries added the SOIC Nominal Body Length to the land pattern name - 
SOIC28P127_1786X1034X264L83X43

To make every component family land pattern name to be symmetrical, we updated the Chip component family names to include the Body Length X Width X Height and added the Nominal Terminal Lead Length - CAPC320X250X120L50

The Chip component family now has the same file name structure as all the other component families except the Pin Qty is suppressed because these are all 2-pin parts. 

Non-standard component families are being introduced every day and there is no guidance in IPC-7351B for non-standard parts. So PCB Libraries created a component manufacturer name Prefix for every component manufacturer. Example: TI is used for Texas Instruments. 

To fix this issue, all non-standard parts which include most connectors, now use the mfr. name and part number (if the part is unique) or the Case Code if the package is shared with multiple part numbers. 

Example of Unique Part Number: MOLEX_47151-0001
Example of multiple part numbers using the same Case Code: TI_CSD25310Q2

By applying these new rules for the land pattern naming convention, we have eliminated all duplicate land pattern names and reformatted the naming convention to be 100% symmetrical for ease of understanding what every value in the land pattern name is. 

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