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bq27541 soldering issue

David Gunderson
Prodigy 180 points
Other Parts Discussed in Thread: BQ27541

We're using the bq27541 in a battery which must pass a very difficult drop test.  We've protected the part from shock as best as we can, but we're still failing solder joints on the Gas Gauge IC pads.  Is there a magic formula for RoHS solder type and re-heat profile that produces an optimum solder joint on this part?

  • 0
    TI__Genius 14985 points

    First, let's start with the standard TI answer for recommended reflow profiles:

    The customer used production reflow profile should be in line with the Jedec Standard profile shown in J-STD020D.1 and not exceeding the given maximum limits. The standard is free downloadable on the Jedec.org web page after free registration.

    http://www.jedec.org/sites/default/files/docs/JSTD020D-01.pdf

    This standard profile is a good start point, in conjunction with the solder paste supplier provided temperature profile recommendation of the used solder paste. The typical peak reflow profile for lead free soldering is in the range of 240-245°C peak temperature measured on the package top side. The above standard stated peak profile is showing the maximum soldering temperature the package can withstand. It should not be the goal to reach this temperature during the customer reflow soldering process. The flux in the solder paste will be used up too quick prior reaching the peak reflow temperature if a too hot profile is used in production, which will yield in less solder wetting on the board pads / component leads.  The final customer profile will depend on the board layout, packages populated on the board and the type of reflow process equipment used.

    If vapor phase soldering is used, commonly 230-235°C medium is used for leadfree (SnAgCu solder alloy) soldering, the process need to allow for a pre heating in this case to minimize the temperature shock. The J-STD020D.1 maximum reflow temperature limits should not be exceeded for vapor phase soldering process.  

    Now, standard aside, there are a lot of other factors that can come into play and a lot of variations to the processes, designs, and materials.  If this standard isn't working for you, let's follow up to analyze your specific data and see if our experts can give you any further recommendations based on prior experience.

  • 0 in reply to dMax
    Prodigy 180 points

    We have found that the solder stencil aperture for this part was wrong. I've instructed the PCA contract manufacturer to correct this issue. For insurance, we're applying glue around the edges of the part after reflow to secure the part to the PCB.

    I'm hoping these actions will result in a more robust mechanical bond between the IC and the PCB.  We'll re-do the drop testing on the new PCA soon.

    Thanks for your help

    --David Gunderson