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I need to buy a batch of UFGBA100 STM32 MCUs from a Chinese broker. I'm concerned that in the quote they specified that the chips will have a date code 19+ (4 years old). How can this affect solderability of the chips assuming assembly in EMS company? Is there some general rule of thumb on how old the chip can be so it can be assembled with reasonably low drop-out rates?

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    \$\begingroup\$ As far as I know, the main risk of old parts is moisture, so if you dry them properly, it should help. \$\endgroup\$
    – Hearth
    Commented Oct 8, 2023 at 22:30
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    \$\begingroup\$ Then just make sure you use fresh solder paste and good flux. There are fluxes sold specifically as "BGA flux" that really do make a difference; a coworker of mine swears by the stuff. \$\endgroup\$
    – Hearth
    Commented Oct 8, 2023 at 22:31
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    \$\begingroup\$ As @Hearth said moisture is the key. Look for the MSL (Moisture Sensitivity Level) and check the manufacturer's website or contact them for recommendations on a baking procedure prior to soldering. \$\endgroup\$
    – John D
    Commented Oct 8, 2023 at 22:47
  • \$\begingroup\$ I contacted my assembly company. They said, that it all depends on the storage conditions of the MCUs. They will bake them before use, but (no surprise) they cannot give any guarantees :/ \$\endgroup\$
    – mactro
    Commented Oct 9, 2023 at 10:50

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