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April 2006

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From:
"Kane, Amol (349)" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Kane, Amol (349)
Date:
Fri, 21 Apr 2006 09:07:13 -0400
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Dear Savants,

Below is my interpretation of this std. Can someone second it and please answer a couple of questions I have? (My interpretation is in bold) I struggled with the std, when trying to justify the need for a desiccant cabinet. according to my interpretation:

1. the components are baked at 125 or 150 dec C within 24 hrs of manufacture (this is MET) and sealed in the MBBs at the component manufacturer before shipping to the customer. the shelf life of the components in the sealed MBB is at least 12 months

2. when the customer opens the MBB, the floor life clock of the component starts. the floor life varies according to the MSL rating. 

For MSL Level 2, 2a and 3
If exposure time <= 12 hrs, 
The FLOOR LIFE can be RESET by placing in a desiccating cabinet capable of maintaining RH <=10% for 5X the exposure time 

If cumulative exposure time < the MSL max specified exposure time, the floor life can be STOPPED/PAUSED by storing in a desiccating cabinet capable of maintaining RH <=10%

(THUS AFTER GREATER THAN 12 HRS EXPOSURE, THE FLOOR LIFE CANNOT BE RESET WITHOUT BAKING, MERELY STOPPED OR PAUSED BY DESICCANT CABINETS)

If cumulative exposure time exceeds FLOOR LIFE by <=72 hrs
OR, If cumulative exposure time exceeding FLOOR LIFE by > 72 hrs, 
bake according to table 4-1 to RESET the floor life. at this point the shelf life can also be reset if sealed again in a MBB


For MSL Level 4, 5 and 5a
If exposure time <= 8 hrs, 
The FLOOR LIFE can be RESET by placing in a desiccating cabinet capable of maintaining RH <=5% for 10X the exposure time 
(THUS AFTER GREATER THAN 8 HRS EXPOSURE, THE FLOOR LIFE CANNOT BE RESET WITHOUT BAKING, MERELY STOPPED OR PAUSED BY DESICCANT CABINETS)

If cumulative exposure time exceeds FLOOR LIFE by <=72 hrs
OR, If cumulative exposure time exceeding FLOOR LIFE by > 72 hrs bake according to table 4-1 to RESET the floor life. at this point the shelf life can also be reset if sealed again in a MBB

J-STD-033B DOES say that a desiccant cabinet capable of maintaining RH level below 5% is equivalent to a MBB. I am not clear on how opening the cabinet doors would affect the components though (anyone who is patient enough to read till this point hazard a guess on this???)

Also, the moisture becomes a problem if the moisture absorbed increases the component wt by 0.1%; if the dry wt of the component is known, then can this be used to decide whether or not the component needs to be baked prior to assembly?? Haven't yet read the J-STD-020 yet, plan to do that today

Thanks in advance,
Amol Kane
M.S (Industrial Eng.)
Process Engineer
Harvard Custom Manufacturing 
941 Route 38  Owego, NY 13827
Phone: (607) 687-7669 x349
[log in to unmask]

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