1. The Tg level is redundant to moisture content or rate of adsorption/drying. In fact, many high Tg boards seem to be more susceptible to high levels of internal moisture adsorption and can delaminate just as easily as low-Tg materials.
2. Not all FR-4 is manufactured the same way. One fabricator may use laminate from many providers, each of which may manufacture the laminate using different processes. They must all meet the requirements of IPC-4101B slash sheets only. There is no guarantee that they will not delaminate easily even if they do meet the requirements.
3. Because there is no classification of PWBs as MSDs (yet), most EMS houses may provide widely varying levels of PWB packaging requirements, and widely varying levels of packaging, handling, and storage methods. My experience with this has been that most EMS providers have an awareness, and attempt to ensure the proper packaging, handling, and storage methods are followed, but it is typically driven by their customers. The EMS quality department is where the task belongs, but most are not at all familiar with MSD practices per J-STD-033 for components, let alone handling, storage, and packaging requirementsfor PWBs.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Schaefer, Chris
Sent: Monday, September 14, 2009 10:02 AM
To: [log in to unmask]
Subject: Re: [TN] Bare Board Moisture Content Standard
Thanks everyone. This information is very useful. Most of our boards are FR4 Tg 170 or higher. Most of the boards have LPI protective masking, with very few boards with unprotected FR4. Obviously the unprotected FR4 have a greater propensity to absorb than the protected, but is it true that not all FR4 is manufactured the same way? Meaning that one made by x manufacture has a different WVTR than another manufacturer? In the same respect, the masking material would have different WVTR as well. Question: do most EMS houses consider bare boards level 2 moisture sensitivity rating or better (polymide, Teflon, etc…)? Curious. Does anyone know when IPC-1601 will be released?
Thank again in advance for your feedback. Acquiring knowing is great!
Best Regards,
Chris Schaefer
Suntron Corporation
Process Engineer
800 N. Brutscher Street
Newberg, OR 97132
Work Phone: 503.554.6270
Cell Phone: 785.248.9016
Email: [log in to unmask]<mailto:[log in to unmask]>
From: [log in to unmask] [mailto:[log in to unmask]]
Sent: Saturday, September 12, 2009 9:38 AM
To: [log in to unmask]; Schaefer, Chris
Subject: Re: [TN] Bare Board Moisture Content Standard
Hi Chris,
The allowable moisture content depends primarily on the temperature your PCB will reach during the soldering process—the higher T the lower the allowable moisture content. some material suppliers make recommendations, see e.g. Isola Technical Belletin, “PCB Packaging for Lead-Free Assembly,” September 2007, 5 pages, available from www.isola-group.com.
Also, I developed a White Paper "Recommendations for PCB FAB Notes and Specifications in Printed Circuit Board Drawings for SnPb and Lead-Free Soldering Assemblies, the Qualification of PCB Shops and Activities to Assure Continued Quality" that among many other things contains an extensive discussion on PCB moisture content.
Werner
-----Original Message-----
From: Chris Schaefer <[log in to unmask]>
To: [log in to unmask]
Sent: Fri, Sep 11, 2009 4:51 pm
Subject: [TN] Bare Board Moisture Content Standard
Hello fellow techies,
My question today concerns allowable moisture content by percentage and if
there is a standard that applies to the varying materials used to make fabs.
We are in the process of creating a flow down document to our board houses
to ensure boards are stored, packaged and20handling appropriately prior to
delivery to us. I have been unable to find a standard that has any information
in regards to this, but have been told there is one. I'm hoping you all couls
shed some light on the subject.
Thanks in advance and have a great weekend.
Ciao!
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