Re: gEDA-user: Baking chips to dehumidify before reflow

[Steve Meier <smeier@xxxxxxxxxxxxxxxxxxx>]

From:
http://smt.pennnet.com/Articles/Article_Display.cfm?&Section=Articles&SubSection=Display&ARTICLE_ID=84836




Baking is a bit more complicated than many people realize. There are
baking recommendations for pre- and post-dry pack based on level and
package thickness. Pre-baking is used to prepare components for dry
packing, while post-baking is used to recondition components after floor
life expiration. Review and follow the time/temperature recommendations
for baking in J-STD-033. Baking temperatures can decrease lead
solderability by oxidizing the leads or causing excessive intermetallic
growth. Do not store components in an oven at baking temperature.
Remember, high-temperature trays can be baked at 125ÂC, while
low-temperature trays cannot be baked at temperatures higher than 40ÂC.

IPC post-bake recommendations after floor life has expired are: 

Package thickness less than or equal to 1.4 mm: For levels 2a through
5a, bake time ranges from 4 to 14 hours at 125ÂC, or 5 to 19 days at 40Â
C. 

Package thickness less than or equal to 2.0 mm: For levels 2a through
5a, bake time ranges from 18 to 48 hours at 125ÂC, or 21 to 68 days at
40ÂC. 

Package thickness less than or equal to 4.0 mm: For levels 2a through
5a, bake time is 48 hours at 125ÂC, or 67 or 68 days at 40ÂC. 




On Thu, 2006-06-08 at 08:58 -0400, Randall Nortman wrote:
> I've got some LQFP chips that I've been storing, with the bag opened,
> for a bit longer than I really should have.  The indicators on the
> humidity cards have started to turn pink, so I'm worried that they
> will have absorbed too much humidity and if I try to reflow them now,
> they'll "popcorn" (i.e., trapped moisture turns to steam and
> evaporates, cracking the package and/or die).  Anybody have any
> suggestions on the best way to do this using common household
> equipment?  I guess I just stick them in an oven at lowish temperature
> for a while, but what temperature and for how long?  I checked the
> datasheets for the chips (Atmel AT91SAM7X256 and Micrel KS8721CL) and
> didn't see any useful information.