Larry,
I could expect that after such long baking of poly PCB moisture is being
removed, but what about solderability??? I believe Pb/Sn finishing could be
still solderable if solder thickeness is thick enough before intermetalic
reach the surface, but what about alternative finishes???
As bare PCB manufacturer we are baking our polyimide boards before HAL, but
less time and lower temperatures you stated. For finished product I cound
not recommend such conditions.
Edward
Edward Szpruch
Eltek Ltd
P.O.Box 159 ; 49101 Petah Tikva Israel
Tel ++972 3 9395050 , Fax ++972 3 9309581
e-mail [log in to unmask]
> -----Original Message-----
> From: [log in to unmask] [SMTP:[log in to unmask]]
> Sent: ו פברואר 14 2003 22:49
> To: [log in to unmask]
> Subject: Re: [TN] Moisture in Raw Boards
>
> Dale,
>
> I see that you did not get a lot of response on this one. I don't believe
> there are any standards on this one, however, I am aware of two studies
> done on the moisture content of polyimide PCB's. One of them I conducted
> myself and the other was done by a major laminate supplier. To say it
> nicely, polyimide is very hygroscopic. Unless the PWB's are stored in a
> vapor proof bag, after it has been fully dried, with Nitrogen you have to
> assume that the PWB has some moisture in the laminate.
>
> Given that assumption, you have three basic choices to make. One, I don't
> care. Two, I care sometimes. Three, the assembled PCB's are so expensive
> I care all the time. If you care all the time, you have to make the
> decision to bake all PWB's since there is no test that I know of to
> determine the moisture content in any one board. Even with the PWB's
> stored in a bag with desiccant it is unreasonable to assume that the
> desiccant will absorb all of the moisture that penetrates the packaging
> unless the material is vapor proof.
>
> Of the two studies I mentioned above, the bakeout cycles came out to be
> 150C for 16 hours or 125C for 24 hours. Following these bakeout
> procedures, the PCB's should be assembled and soldered within 8 hours from
> coming out of the oven. At 72F and a relative humidity of 50% the PWB
> will regain 50% of the moisture lost within 24 hours.
>
> Larry
>
> PS - I believe I visited your plant about a year ago representing a PWB
> supplier.
>
>
> In a message dated 2/11/03 1:54:22 PM Central Standard Time,
> [log in to unmask] writes:
>
>
>
>
>
>
> I, and our board suppliers, have looked through IPC-6011, 6012, 600,
> 610 and
> most of the other pertinent standards and cannot find an answer to
> this
> question:
>
> How long should multi-layer printed circuit boards be left out in a
> controlled ambient environment (standard factory temp/humidity)
> before
> pre-baking the boards becomes necessary to dry out any accumulated
> moisture
> in them? We would like to minimize potential board delamination due
> to
> trapped moisture in the FR4 or polyamide layers (which can expand
> rapidly
> when the board is placed through a reflow oven or solder wave).
>
> Does anyone want to wade in on this one? We have identified a
> standard for
> pre-baking IC components before use in this type of high-heat
> environment,
> but cannot find any standard or specification pertaining directly to
> PCBs
> themselves. I suspect it will have to take into account the material
> used,
> number of layers, the definition of "standard factory temp/humidity"
> and
> other things related to the board and the environment it is stored
> in prior
> to use.
>
> Any help in this regard would be appreciated.
>
> Thanks!
> Dale Ritzen
> Quality Manager
> Austin Manufacturing Services
> 9715A Burnet Road, Suite 500
> Austin, TX 78758
>
>
>
>
>
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