Good morning Victor,

Our internal PCB manufacturing workshop as well as our usual CPB subcontractors gave us the rule of thumb that mixed materials/flexes shall be reflowed within 6h after baking/complete moisture removal. So, if I translate it into IPC MSD classification it becomes an MSL6 part with 6h floor life - not shelf life, sorry for the wrong wording.
As long as assembly floor people are supposedly trained to MSD handling accordingly, we considered classifying those special stack-ups this way was the most efficient in order to avoid any bad (and costly) surprises.

On a side note, this might as well be applicable to mixed rigid materials, not only flexes, but this is another story.
Regards
sylvain

-----Original Message-----
From: TechNet <[log in to unmask]> On Behalf Of [log in to unmask]
Sent: 10 January 2020 16:08
To: [log in to unmask]
Subject: Re: [TN] Flexible PCB's

Sylvain,

   Clarification on this statement " MSL6 parts with 6h shelf life"  especially the 6h......

Victor,

-----Original Message-----
From: TechNet <[log in to unmask]> On Behalf Of Sylvain Kaufmann
Sent: Friday, January 10, 2020 7:42 AM
To: [log in to unmask]
Subject: Re: [TN] Flexible PCB's


[EXTERNAL EMAIL] 

Dear Jerry,

We regularly assemble multilayer flex or flex-rigid boards and handle them as MSL6 parts with 6h shelf life prior to reflow. As far as I understand it, according to J-STD-0033 baking is mandatory for MSL6 devices no matter how they are packed, so we do.
We also ask our subcontractors to do so when outsourcing this kind of assembly.

I agree it might look highly conservative, though, but our internal PCB manufacturing workshop expert confirmed we'd better do so.

So far we never faced any issues this way on few thousands we had the chance to handle.

Best regards
Sylvain Kaufmann

-----Original Message-----
From: TechNet <[log in to unmask]> On Behalf Of Jerry Dengler
Sent: 10 January 2020 13:53
To: [log in to unmask]
Subject: [TN] Flexible PCB's

TechNetters,
 
We reviewed documentation from a flexible PCB manufacturer and saw that they recommend baking of the flex boards prior to assembly even if they are brand new boards in a Moisture Barrier Bag.
Why wouldn't these be handled like any other moisture sensitive component?
How many of you that work with flexible PCBs are baking them even if they come out of a MBB with A HIC card that shows no real moisture?

Thank You,

Jerry Dengler

Production Manager

Pergamon Corporation

380 Crooked Lane, Unit# 3

King of Prussia, PA  19406-2567

U.S.A.

(610) 239-0721 Phone