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Doesn't happen every day.. IC package destroyed while hot air soldering.

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Eka:

--- Quote from: westfw on September 06, 2018, 08:22:01 am ---I didn't realize that moisture would end up being a problem with "hand" soldering of SMT components :-(I knew it was an issue with full industrial reflow equipment...)

--- End quote ---
Think about the physics of it. Using hot air around and over the case of chip to desolder or solder it is just like putting it into a reflow oven. It will use up one of the reflow cycles the chip is rated for, and usually they are rated for 1 to 3 cycles. I've never seen higher. Also any moisture gain the chip had will need to be countered if the case is moisture sensitive. So baking out the moisture is needed before soldering or desoldering with hot air. Thermal shock and differential temperatures in the case is also an issue. It is best to warm up the whole board first. That way the temperature difference between the top and bottom of the case is less when it is reflowed.

The reflow oven temperature curves all have a more gentle warm up and soak period before a relatively fast rise to solder melting temperatures, then cool down after. The time spent at solder melt temperatures is an issue. Often it is limited to only 15 to 45 seconds.

As for baking out, it can be done at various temperatures, and that effects how long it takes. I saw in one TI doc that 40C was the maximum bake out temperature for parts in reals, and trays. Sometimes the manufacturer will have different reflow curves and maximum temperatures for different moisture exposure levels.

This TI doc show the requirements for their power modules. It even has an overall time limit for start to end of reflow soldering cycle.
http://www.ti.com/lit/an/slva840/slva840.pdf

Then there are the temperature handling issues of the other parts on the PCB. Lithium batteries are something that can't even be heated to bake out temperatures, let alone reflow temperatures. So they need to be removed before baking out the moisture. They also need shields to protect them if using hot air near them.

Yansi:
Me and my friend have once been dismantling an old 48 port ethernet switch, removing all interesting components from the board. There was a metric shit ton of synchronous RAM chips and when heating one of these, it popped right in half with a hole in the middle.  :-DD Never experience this before. We were baffled by that.

exe:
> they were kept inside the tape, inside the antistatic bag.

That's a bummer, I store all my stuff almost like you and hoped I was protected from pocorn problem. Worse yet, I thought it's enough to bake just for 1h at 90C, didn't know it might not be enough.

I wonder if IC can be damaged this way, but continue to work somehow (and fail or malfunction later). Perhaps, this is possible.

CatalinaWOW:
ICs can be damaged this way and continue to work for a while, but it is relatively rare.  You were lucky in a way that one of them blew right open and made the diagnosis obvious.  It is pretty common for popcorning to kill the chip without visibly damaging the package.  Diagnosis can be a real head scratcher if you don't have a chip failure diagnosis lab at your disposal.

Anti-static bags often provide no meaningful seal once opened.  Even the ones with a ziplock fastening can leak like a sieve.  A dessicant bag can help, but can saturate fairly quickly.  A lot depends on your environment. 

Manufacturers usually provide a bakeout procedure for the packages they use.  In some cases it may vary from the JEDEC standard.

JS:
Could this be a problem while soldering with an iron?
While reworking on a PCB, for removing a dead IC with hot air, what should be done to prevent this from happening to the surrounding parts? Bake the PCB before reworking? What about hot air reflowing, with an oven or a reballing process?

I was aware of this, I just don't know how to deal properly in repair process, a lot of info about this for manufacturing process but I haven't seen much about reworking...

JS

EDIT: just found this http://www.ti.com/lit/an/slva439a/slva439a.pdf

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