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MSP430FR6043: PCB: Direct connect vs relief connect.

Intellectual 410 points

Replies: 2

Views: 64

Part Number: MSP430FR6043

Hi,
 
 There are two ways to connect the GND pad to the GND plane:
 - direct connection
 - relief connection

I understand, that the „relief connection” has to be used for thermal isolation of the pad and the copper plate.
When using SMT soldering, the PCB board is heated almost evenly, so thermal relief isn't generally needed here.
Therefore, I wonder, if it is a good simplification to use a direct connection for SMT soldering and relief connection for THT soldering?
 
Would you give me recommendations on this subject or would you direct me to any application note in which this subject was discussed?

/Adam

  • Hi Adam,

    The approach with the thermal-groud-pad (this is the name I learned in the old days) is good for hand soldering, and it is perfect if you would need to rework your PCB. For signals with really high frequency components >GHz it shows some disadvantages. All that is true for large geometries. If you go for tiny structures e.g. SMT you will find out that the thermal grounds might not have four spokes available anymore. Some layout tools show only one. I've seeen one that generated a electrical disconnect. Run your DRCs afterwards...

    A direct ground connection is the better choice... is the manufacturing process allows that. You usually have some temperature ramps where the whole PCB including components is heated up to 150C or so; then the temp ramp for the actual soldering aplies enough heat for the melting process. Here you can x-check with your manufacturing service.

    Also for hand soldering and reworking the direct connection is no problem. I used to work with a hot sand bed in which the PCB (with components) was heated up to 150C. At that temperature most components (incl LEDs & plastic switches) do not suffer to much yet. Hand soldering with an preheated PCB is really easy also with direct ground connects. But wear leather gloves, it could be painful elsewise.

    Meanwhile you will find infrared reworking stations tha also have not problems to pre-heat the PCB with components to 150C for eady fixxes.

    Thermal ground pads have its advantages for the manufacurer. For the FR604x devoces I do not see an electrical advantage. For other components on your PCB that have a large thermal mass things might be different.

    I hope I could help a little

        have a nice day

          Johann 


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  • In reply to Johann Zipperer:

    Hi Johann,

    I appreciate your help and expertise.
    This explanation is realy profound.

    Adam

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