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8802 Views 14 Replies Latest reply: May 7, 2014 3:56 PM by cgb1776 RSS
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Apr 16, 2014 10:47 AM

Fine pitch soldering issues

On a current project, I'm soldering this header on a board: http://www.digikey.com/product-detail/en/BM10B(0.6)-20DP-0.4V(51)/H11951TR-ND/2712174

 

The header seems great, it's small and low profile, perfect for this application.  However, I'm having some serious issues with the soldering due to the very fine 16 mil pitch.  My first revision of the board I tried to apply solder paste by hand and I kept getting solder bridges on my boards.  I marginally lengthened the pads from the manufacturer's recommendations with the second revision in the hope that the solder would flow out along the pads versus jumping the soldermask between the pads.  I also got a stencil to better control the amount of solder paste I applied on each pad. But I'm still getting a lot of bridging!

 

It's lead free solder, as I'd like the end product to be RoHS compliant. 

 

Any tips on what I could do from a design and execution standpoint to get this right?  Do I lenghten the pads more?  Should I shrink them?  Should I have the stencil holes made smaller?  Do I need to change my heating profile?

 

Help would be appreciated - thanks!

 

-John

  • papalyle Novice 55 posts since
    Apr 6, 2014
    Currently Being Moderated
    Apr 18, 2014 8:07 PM (in response to JohnDavis)
    Fine pitch soldering issues

    John,

     

    How about applying just a big enough glop of solder to a short copper wire and just transfering that much to the pads.

     

    papalyle

  • davecuthbert Apprentice 87 posts since
    Feb 18, 2014
    Currently Being Moderated
    Apr 20, 2014 10:53 AM (in response to JohnDavis)
    Fine pitch soldering issues

    I suspect that reducing the solder paste volume will solve the bridging issue.

  • papalyle Novice 55 posts since
    Apr 6, 2014
    Currently Being Moderated
    Apr 20, 2014 9:24 PM (in response to JohnDavis)
    Fine pitch soldering issues

    why waste solder paste also, try it

     

    papalyle

  • chucka2420 Novice 2 posts since
    Apr 23, 2014
    Currently Being Moderated
    Apr 23, 2014 10:05 AM (in response to JohnDavis)
    Fine pitch soldering issues

    Liquid flux in a nail polish container is the answer to all your fine pitch soldering issues. (both reflow and hand solder)

      • chucka2420 Novice 2 posts since
        Apr 23, 2014
        Currently Being Moderated
        Apr 23, 2014 3:07 PM (in response to JohnDavis)
        Fine pitch soldering issues

        The flux came in a chem type bottle and I would pure it into a nail polish container for use. When hand soldering a QFP or a SMT connector I would apply a tiny bit of solder to the two most opposite pads (just to hold the device in place and lined up with the pads). Then using my "nail polish" wipe a healthy amount of flux clear across all the pins. Then using a small soldering tip heat up each pad barely touching the very end of the components pin and solder each pin. If you get a solder bridge at this point no problem. Once the component is soldered correctly I apply a little more flux clear across all the pins again right on top of all the pins and solder bridges. Then over each bridge or connection with too much solder you can wipe the bridge away running the iron parallel away from the device along the pins. If there is WAY too much solder you can get rid of it with a little copper braid.

         

        As far as the type of flux, I have no idea to be honest. All I know is that I was using normal solder (lead/tin, 80/20 i believe) (I did not care about ROHS) because the lead free solder sucks. The flux was certainly NOT no-clean. I left a mess behind on the PCB (but the device was solder perfectly). I would clean up using a spray can of flux off, a chem wipe, and a short brisel chem brush (that made it spotless). The flux was 10W 30 motor oil consistancy.

        I bought it from Techni-Tool, standard, nothing special, probably the most expensive since I worked for the government and money was no object. lol

         

        As far as pad size on the PCB, Solder Mask layer, solder paste stencil, I have some of my own tricks of the trade that help certain problems depending on if the component is a QFP, BGA, or connector, if my board is being machine build by a pick and place robot, if the solder paste if being applied by a wiping action on a stencil or not, etc etc. But normally pad size is determined by lead shape and footprint by the manufacturer. I may alter the footprint slightly if I know I am going to hand solder these devices.

         

        Hope that helps

          • davecuthbert Apprentice 87 posts since
            Feb 18, 2014
            Currently Being Moderated
            Apr 28, 2014 12:04 PM (in response to JohnDavis)
            Fine pitch soldering issues

            You have no bridging because you don't have much solder. But does the solder fillet meet IPC guidelines?

        • cgb1776 Novice 2 posts since
          Apr 30, 2014
          Currently Being Moderated
          Apr 30, 2014 12:04 PM (in response to chucka2420)
          Fine pitch soldering issues

          I hand solder 100 pin TQFP chips (8mil pads).

          I use chip quik solder paste and chip quik flux (both from a syrnge). Prior to placing the chip I squeeze some flux on a peice of plastic then squeeze a tiny bit of solder into the flux. Mix for a bit, then apply to pads. I dont have a toaster over to reflow things (yet) so I tack each corner pin to stabilize the chip then either use reflow hot air station to melt with hot air, or use a fine tip iron to make the remaining solder connections.

          Using a 5x magnifying lamp to do the work, then placing another hand magnifying glass on top of the lamp lens to check my work helps very much!

          • mee2 Novice 1 posts since
            May 6, 2014
            Currently Being Moderated
            May 6, 2014 4:40 PM (in response to cgb1776)
            Fine pitch soldering issues

            you said that you solder 100 pin TQFP chips and that you use chipquick solder paste , and chipquick flux , could you give me the part no. for those so i can order me some. I would like to try that,

            • cgb1776 Novice 2 posts since
              Apr 30, 2014
              Currently Being Moderated
              May 7, 2014 3:56 PM (in response to mee2)
              Fine pitch soldering issues

              I dont have the original part numbers but I just recieved my digikey order today that just so happened to have an order of paste and solder. The part numbers I ordered were... solder: SMDLTLFP ,  flux paste: SMD291NL.

               

              I haven't used these specific items yet, but I'm sure they will work as good as the last stuff I bought.

  • MiracleMark Novice 1 posts since
    Apr 30, 2014
    Currently Being Moderated
    Apr 30, 2014 12:10 PM (in response to JohnDavis)
    Fine pitch soldering issues

    Hi John:

     

    http://store.curiousinventor.com/guides/how_to_solder/kind_of_solder/

     

    Here's a tutorial on soldering and solder; well worth the price.  Also on youtube are numerous rework and fine pitch soldering techniques. I've soldered over 100,000 connections and would never try to hand solder that fine pitch.  If you have a stencil, your're half way to success.  You need to reflow that component.  Until we bought a fancy-schmancy reflow oven here at Miracle Audio, we would reflow by hand using a hot air rework tool, and there are some vids on using a standard hot air gun, but I wouldn't recommend that for this fine pitch.  The most important thing you need is a great reflow solder that includes a flux.  We use Cookson no-cleanAlpha SAC-305.  It might not be exactly what you need but there are dozens of great tin/copper/silver alloys that qualify for RoHS.  Do some research and watch some videos.  The time spent learning will save you a lifetime of screw-ups.  Good luck!

     

    Mark

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