• State Resolved
  • Locked Locked
  • Replies 3 replies
  • Subscribers 83 subscribers
  • Views 907 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TMS320F2809: TMS320F2809ZGMA

Green Deng
Expert 4490 points
Part Number: TMS320F2809


 We are using Microcontroller TMS320F2809ZGMA from TI which is MSL 3 rated. After we took it out from MBB(Moisture Barrier Bag), we do reflow soldering at 260 degC with in 7 days and our environment conditions are <30 C/60H. After assembly , we ship the board to our vendor for PCB molding. Molding process is done at 220 degC . Duration between Reflow and start of Molding process is 2 to 4 weeks.

Will be there any Yield or Latent(Reliability) issues, as Floor life of MSL 3 rated component is just 7 days(168 Hrs)?]

  • 0
    TI__Intellectual 1750 points

    TI document SPRABY1 section 2 has some discussion about applying moisture sensitivity rating. The shelf life MSL3 applies a standard of 1 week at 30C/60%.

    However per JEDEC specification IPC/JEDEC J-STD-033C Table 7-1, if your actual conditions on the factor floor is less than 30/60 RH%, then that floor life from bag open may extend out beyond that 1 week. For example if it is actually 25C max and controlled to be 50% RH max, then 1 week may become 2 weeks or a BGA where body size is < 1mm. 

    As for the later PCB molding process, you mention this it is at 220C. ( I am assuming this is NOT a reflow type of profile which SPRABY1 discusses in section 4).

    When the industry went from leaded to leadfree solder, a rule of thumb was a when it went up from 220-235C type of leadfree peaks to 260C temperature, then a package may drop down an MSL level (eg/ MSL2/220C became MSL3/260C). Thus, it can be argued that it works the other way - an MSL3/260C becomes an MSL2/220C. 

    Secondly, the focus on temperature exposure is usually on the peak tempeatures for soldering but the ramp up and cool down rates are also important for avoiding internal damage or soldering issues. In this instance, you should look at your time to ramp from ambient to 220C. If too rapid, you may still get a problem where any internal moisture may turn to steam at the same time while plastic package is trying to expand. 

    There is no mention about any storage/shipping medium for the after reflow/ before molding PCBs but I am assuming this prevents further moisture exposure. If it does, then a controlled molding 220C process is likely to be ok. If this 220C molding process is new to you, then I'd recommend submitting some units to a SAM inspection or cross sectioning to validate no internal delamination of the semiconductors/

    PS: note your 220C is slightly above 217C which is regarded as being the liquiduous temperature for a SAC solder ball. If you are not careful in your molding process, you may weaken the original solder joints.

  • 0 in reply to Krishnamoorthi Subburaj
    TI__Intellectual 1750 points

    Your reflow process sounds ok but don't you to be sharing any proprietary information on the yield loss or the injection process itself in an open forum so lets discuss further via email.

    My email address is awebber at ti.com