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LM317A: LM317AT/NOPB(TO-220 package) assembly order for the device soldering to board with heat sink.

Kazuya Nakai59
Guru 20975 points
Part Number: LM317A

 Hello guys,

 One of my customers is going to use LM317AT/NOPB for their new products.

 They have the following question about the device assembly order for the device soldering to board with heat sink. Could you please give me your reply?

 Q. They will build LM317A up with a heat sink as the picture in the following URL.

 http://www.aitendo.com/product/13911

 They want to build it up with the following order.

 1. Form LM317A(TO-220) leads like "L" letter.

 2. Place the heat sink on the board.

 3. Insert formed LM317A to 3 through holes.

 4. Screw the LM317A and heat sink to the board with bolt and nut.

 5. Solder LM317A to the board with flow soldering (wave solering).

 Is this order problem? Should screwing be after soldering?

 Also is it no problem to solder LM317AT/NOPB base on the following doccumantation?

 AN-2029 Handling and Process Recommendations

http://www.ti.com/lit/an/snoa550f/snoa550f.pdf

 Your reply would be much appreciated.

 Best regards,

 Kazuya.

 

  • 0
    TI__Mastermind 45440 points

    Hi Kazuya-san,

    I believe the proposed assembly flow is the correct one. My reasoning is simply that wave soldering after the device is already mounted and screwed to the heat sink might be less stress on the device than screwing it down after going through the solder wave. 

    Yes, please follow the recommendations of AN-2029 for your wave soldering profile. 

    I hope this helps.

    Regards,

  • 0 in reply to JCHK
    Guru 20975 points

     Hello John,

     Thank you very much for your prompt reply.

     Could I ask you an additional question as the follow?

     Q. When LM317T is soldered after screwing it down, the customer think the device temperature becomes higher than no screwing case during flow soldering.

         Is the device no damage even if the device temperature is higher as long as following AN-2029 for the flow soldering?

     Thank you again and best regards,

     Kazuya.

  • 0 in reply to Kazuya Nakai59
    TI__Mastermind 45440 points

    I Kazuya-san,

    The expert recommendations I see mostly point to fasten first then solder. See the recommendations here: http://www.circuitnet.com/experts/86347.html

    The common reason given is that fastening after soldering can add stress to the solder joints. Again, this is very subjective as it depends on your manufacturing flow, how well the torque of the screw is controlled and likely the materials used. 

    I hope this helps.

    Regards,

     

  • 0 in reply to JCHK
    Guru 20975 points

     Hello John,

     Thank you very much for your reply. I could understand well that it is better to screw the device down before soldering.

     Could you please give me your comment for the following question?

     Q. Is LM317A(TO-220) no damage in soldering as long as following to AN-2029 and the device absolute maimum ratings (Lead temperature is less than 260C degree (4 seconds)?

          AN-2029: http://www.ti.com/lit/an/snoa550g/snoa550g.pdf

          LM317A absolute maximum rating in the device datasheet.

     Could you give me your comment to get this device adoption to the customer products?

     Thank you again and best regards,

     Kazuya Nakai.

  • 0 in reply to Kazuya Nakai59
    TI__Mastermind 45440 points

    HI Kazuya-san,

    As the application report states:

    We cannot provide a general soldering recommendation. There are simply too many unknowns.

    The guideline in the datasheet is there to help make sure that the device is not physically damaged:

    The application report AN-2029 shows a profile where the peak temperature for a lead-free wave-solder profile exiting the wave is 250C. 

    I hope this helps.

  • 0 in reply to JCHK
    Guru 20975 points

     Hello John,

     Thank you very much for your strong support.

     I could understood well and I will explain it to the customer.

     Thank you again and best regards,

     Kazuya.