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large power traces and small SMD devices

Former Member

I'm relatively new to working with SMD devices, and I'm designing a board

that has a mix of SMD and through-hole. Generally I throw down the largest

traces I can get away with, in particular for power and ground. As such my

board uses a 36mil power/gnd and 10mil signal traces. I added a QFN28

package with 0.8mm (31.5mil) spacing and the autorouter had a fit dealing

with it. I don't need those big fat traces going to the little SMD package,

but I wouldn't mind keeping them for the rest of the layout.

 

Is there a way to specify this? For example to use a different net class to

connect the SMD device's power pins than the rest of the devices?

 

Thanks,

Scott

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  • scott baker schrieb:

     

    I'm relatively new to working with SMD devices, and I'm designing a board

    that has a mix of SMD and through-hole. Generally I throw down the largest

    traces I can get away with, in particular for power and ground. As such my

    board uses a 36mil power/gnd and 10mil signal traces. I added a QFN28

    package with 0.8mm (31.5mil) spacing and the autorouter had a fit dealing

    with it. I don't need those big fat traces going to the little SMD package,

    but I wouldn't mind keeping them for the rest of the layout.

     

    Is there a way to specify this? For example to use a different net class to

    connect the SMD device's power pins than the rest of the devices?

     

    Routing manually perfectly solves this (and other) problems.

     

    If you really want to use the autorouter, route at least the supplies

    manually.

     

    Tilmann

     

  • On 5/1/2010 3:06 AM, Tilmann Reh wrote:

    scott baker schrieb:

     

    I'm relatively new to working with SMD devices, and I'm designing a board

    that has a mix of SMD and through-hole. Generally I throw down the largest

    traces I can get away with, in particular for power and ground. As such my

    board uses a 36mil power/gnd and 10mil signal traces. I added a QFN28

    package with 0.8mm (31.5mil) spacing and the autorouter had a fit dealing

    with it. I don't need those big fat traces going to the little SMD package,

    but I wouldn't mind keeping them for the rest of the layout.

     

    Is there a way to specify this? For example to use a different net class to

    connect the SMD device's power pins than the rest of the devices?

     

    Routing manually perfectly solves this (and other) problems.

     

    If you really want to use the autorouter, route at least the supplies

    manually.

     

    Tilmann

    i would manually lead out the small traces and then let the autorouter

    finish with thicker ones. it won't touch anything you've already done.

    remember to save your manually routed board in case you make mistakes, i

    don't know if ripup will kill your manual work as well as autorouter.

     

    also crucial for autorouter ( and manual router too! but different

    setting..) is size of routing grid must be 5-10 times finer than the

    pitch of the connections so it can weave them in.