From the CAD Library: Padstack Naming Convention, Part 3


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Over the past two columns, we looked at padstack naming conventions, and some details. This week, I’ll finish up the topic. Let’s look at corner modifiers.

Chamfered and rounded corner modifiers are used to indicate which corners are modified. Figure 1 shows the “order of precedence” that has been given to the first four modifiers.

 

Figure 1.

Modifiers:bl – bottom leftbr – bottom rightul – upper leftur – upper rightulr – upper left & rightblr – bottom left & rightubl – upper and bottom leftubr – upper and bottom right

Rounded and chamfered lands in “one corner” modifier examples:

r100_200rbl50 = rectangular land 1.00 x 2.00 with 0.50 radius for rounded corner in bottom left corner

r100_200rbr50 = rectangular land 1.00 x 2.00 with 0.50 radius for rounded corner in bottom right corner

r100_200rul50 = rectangular land 1.00 x 2.00 with 0.50 radius for rounded corner in upper left corner

r100_200rur50 = rectangular land 1.00 x 2.00 with 0.50 radius for rounded corner in upper right corner

r100_200cbl50 = rectangular land 1.00 x 2.00 with 0.50 chamfer for chamfer corner in bottom left corner

r100_200cbr50 = rectangular land 1.00 x 2.00 with 0.50 chamfer for chamfer corner in bottom right corner

r100_200cul50 = rectangular land 1.00 x 2.00 with 0.50 chamfer for chamfer corner in upper left corner

r100_200cur50 = rectangular land 1.00 x 2.00 with 0.50 chamfer for chamfer corner in upper right corner

The chamfered and rounded rectangular with all four corners chamfered does not need a corner modifier.

Modifier examples with rounded rectangle land shape: 

r100_200r50 = rectangular land 1.00 x 2.00 with 0.50 radius for rounded corners in all 4 corners

r200_100r50 = rectangular land 2.00 x 1.00 with 0.50 radius for rounded corners in all 4 corners

Modifier examples with chamfered rectangle land shape: 

r200_100culr50 = rectangular land 2.00 x 1.00 with 0.50 chamfer for chamfered corners in 2 corners

r200_100c50 = rectangular land 2.00 x 1.00 with 0.50 chamfer for chamfered corners in all 4 corners

Thermal pads can have a combination of chamfered and rounded corners; however, the typical application is two variations. The most prominent is a chamfered corner located near pin 1, and the second is a chamfered corner located near pin 1 with the other three corners rounded. These two variations are the default.

Square Configurations

s480p4s152 = 4.80mm square land with four paste mask squares measuring 1.52mm each

u480p4s152cul50 = 4.80mm square land with four paste mask squares of 1.52mm each with 0.50mm chamfer in upper left corner

u480p4s152cul50r25 = 4.80mm square land with four paste mask squares 1.52mm each with 0.50mm chamfer in upper left corner with 0.25mm corner radius

Example of a local fiducial for fine pitch SMT components:

c100m200k200 = Circular land 1.00 with solder mask 2.00 with keep-out 2.00

s100m200k200 = Square land 1.00 with solder mask 2.00 with keep-out 2.00

See Figure 2 for local fiducial application used for fine-pitch components.

 

Figure 2.

That concludes the treatise of padstack naming conventions. Next week, we’ll move into solder joint integrity.

Tom Hausherr, CID+, is EDA library product manager for Mentor Graphics Corporation. To follow him on his blog, click here

Did you know that you can download a free 10-day trial license for the LP Wizard by clicking here? After the 10-day trial license ends, the LP Wizard will run in demo mode as an IPC-7351B LP Calculator. The LP Calculator auto-generates padstack names using the convention mentioned in this article.

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