Manon,

There are several questions to ask first when establishing retention
times for your in-house material controls.

1. Do you properly maintain the environment, where the component will be
retained, 70F 5F 50RH?
2. If not, then do you use desiccants and/or Oxidation Arrest Paper in
each ESD bag to minimize die moisture absorption and free oxides?
3. When determining retention times, do you base it on the suppliers
date code or on your internal retention times. There are some hard to
come by components
 that are sold by Brokers. These parts may have sat at an un-disclosed
site with poor retention procedures and with a 1195 (wwyy) date code.
4. Because of oxides, do you establish guidelines for your purchasing
department to only buy certain devices with x date code. (i.e, Actives
with at least 12
 months remaining from the date they were manufacturing, assuming a 24
month retention time. Less than this will require engineering review to
see if there
 where problems in assembly associated to this part. Passives, same
way).
5. DO NOT over look PCBs that should follow the same criteria. Evaluate
your PCB supplier to insure they retain overage material properly. You
never know when you
 have to go back and request the overage, you'll get a big surprise if
the material was not stored properly.
6. Most importantly, what type of Solderpaste and Flux are you using.
You allow yourself a wider process window when using OA fluxes versus
no-clean. Your process
 window narrows greatly when using no-cleans. You must pay particular
attention to all variables introduced to the assembly set-up.
7. Re-consider baking PCBs and Components! I am against the practice.
Proper retention should be established first, versus trying to fix a
problem that could
 only get worst. Think IMC when baking PCBs and Components.
Intermetallic Compounds only worsen as temperature and humidity
increase, thus the solderability is
 substantially reduced.

Hope this helps,

John Gulley
Director of Technology and Marketing



-----Original Message-----
From: Manon Dutil [mailto:[log in to unmask]]
Sent: Tuesday, August 24, 1999 6:23 AM
To: [log in to unmask]
Subject: [TN] old date codes


Hi technetters,

What is an acceptable date code on a resistor or cap for commercial use,
3 years old or 5 years old ?


Manon Dutil
Product Manager
[log in to unmask]
819-569-9561 tel
819-569-8222 fax

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