TECHNET Archives

November 2011

TechNet@IPC.ORG

Options: Use Monospaced Font
Show Text Part by Default
Show All Mail Headers

Message: [<< First] [< Prev] [Next >] [Last >>]
Topic: [<< First] [< Prev] [Next >] [Last >>]
Author: [<< First] [< Prev] [Next >] [Last >>]

Print Reply
Subject:
From:
"Stadem, Richard D." <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Stadem, Richard D.
Date:
Thu, 17 Nov 2011 17:29:46 -0600
Content-Type:
text/plain
Parts/Attachments:
text/plain (152 lines)
Careful, many components will fail if exposed to 125C for 24 hours. The specific component data sheets and J-STD-030 provide a number of recommended bake temperature/time schedules for various components, with the J-STD-030 being a guideline, not requirements. Even for components you do not want to bake at too high of a temperature or for too long. In fact, the same methods outlined within IPC 1601 can be used for determining the optimum bake schedule and storage practices for components, but that topic is separate to the discussion of bake schedules for PWBs.

-----Original Message-----
From: Ahmad, Syed [mailto:[log in to unmask]] 
Sent: Thursday, November 17, 2011 4:44 PM
To: TechNet E-Mail Forum; Stadem, Richard D.
Subject: RE: [TN] Recommended Bakeout Temperature for Boards and Assemblies

I am not sure about how many can access it online but "Finite difference modelling of moisture diffusion in printed circuit boards with ground planes" by O. Thomas, C. Hunt, M. Wickham, National Physical Laboratory, Hampton Road, Teddington, UK, to be printed in Microelectronics Reliability, has an interesting graph showing how the moisture ingresses and dissipates over time at 125C. Moisture contours are shown as well.

Leaving how much moisture in a PCB may not be a problem should be different for each design depending upon their thickness, layers, amount and distribution of metal, etc. 

The bake out recommendation for devices, which go on PCBs, seems to be a standard 24 hours bake at 125C.

Syed Sajid Ahmad

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Stadem, Richard D.
Sent: Thursday, November 17, 2011 4:21 PM
To: [log in to unmask]
Subject: Re: [TN] Recommended Bakeout Temperature for Boards and Assemblies

105 C is pretty much the standard pre-bake temp in the industry, at least in the Upper Midwest. I can rattle off more than 20 companies that use a 105 bake temp for anywhere from 4 to 24 hours to pre-bake FR-4 PWBs prior to processing. 125 C is a little high, and is much too high for IAg finished PWBs. They will come out tarnished yellow after only 6 hours @ 125 C. Immersion tin or Lead-free HASL almost cannot be baked, or they come out almost black after 12 hours at 125 C. Standard Sn63 HASL definitely turns a darker shade of gray when baked for more than 8 hours at 125C. So the bake schedule (time/temp) should also be based on the surface finish of the PWB. I would not have an issue with baking ENIG @ 125 C, except once again, it can exacerbate nickel issues of they are not plated properly to begin with. 

So 105 is, at least to me, a good general bake temp.

When process engineers see this darker shade of gray, they themselves turn a whiter shade of pale.

The most important part of the bake schedule is that the minimum required bake time should be established, and that is what we focused on in IPC 1601. It provides the methods for determining the optimum bake time to get to a 20% of saturated weight moisture content, typically considered safe for most if not all reflow or soldering processes with FR-4 PWBs. 

PEN, Polyimide, CEM, and other PWB materials may need a lower moisture content limit, such as less than 5% of saturated weight. Again, the methods listed in IPC 1601 provide the tools for determining the moisture content and rate of moisture removal, as well as rate of moisture re-adsorption from a completely dry state (answers the question of "how long can I leave a given PWB out at a given humidity level"?) 

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of R Sedlak
Sent: Thursday, November 17, 2011 3:22 PM
To: [log in to unmask]
Subject: Re: [TN] Recommended Bakeout Temperature for Boards and Assemblies

I suspect 125 C is very close to ideal.
Rudy Sedlak

--- On Thu, 11/17/11, Garcia, Rigo (GSFC-300.0)[MANTECH SRS TECHNOLOGIES] <[log in to unmask]> wrote:

From: Garcia, Rigo (GSFC-300.0)[MANTECH SRS TECHNOLOGIES] <[log in to unmask]>
Subject: Re: [TN] Recommended Bakeout Temperature for Boards and Assemblies
To: [log in to unmask]
Date: Thursday, November 17, 2011, 10:34 AM

Thank you Rudy,

Very interesting. I am an Electrical Engineer, so, I am not familiar with the concept of chemical bonding of the water. I always saw the delamination problem as a natural result caused by the water evaporating.

What do you think is the "sweet point" regarding temperature where you can safely drive the water out without risking causing damage to the PCB due to quick release of water vapor?

Best regards,

Rigo

Sr. Quality Assurance Engineer
Workmanship Standards, Code 300
NASA, Goddard Space Flight Center
Greenbelt, MD  20771
Phone. (301) 286-6129
Fax.       (301) 286-6576

From: R Sedlak [mailto:[log in to unmask]]
Sent: Thursday, November 17, 2011 1:12 PM
To: TechNet E-Mail Forum; Garcia, Rigo (GSFC-300.0)[MANTECH SRS TECHNOLOGIES]
Subject: Re: [TN] Recommended Bakeout Temperature for Boards and Assemblies

Rigo Garcia:  First, you are assuming that the water in the board has the same characteristics as liquid water.  It does not.  The water is chemically bonded, and needs more than 100 C to be driven off.   Second, 125 C is gentle, compared to the temperatures the board will see during soldering.

Rudy Sedlak
RD Chemical Company

--- On Thu, 11/17/11, Garcia, Rigo (GSFC-300.0)[MANTECH SRS TECHNOLOGIES] <[log in to unmask]<mailto:[log in to unmask]>> wrote:

From: Garcia, Rigo (GSFC-300.0)[MANTECH SRS TECHNOLOGIES] <[log in to unmask]<mailto:[log in to unmask]>>
Subject: [TN] Recommended Bakeout Temperature for Boards and Assemblies
To: [log in to unmask]<mailto:[log in to unmask]>
Date: Thursday, November 17, 2011, 8:28 AM Good day TechNetters!

I have been reading all sorts of materials regarding bakeout of boards and the consequences. Among some of the documents I've read is IPC-1601 - "Printed Board Handling and Storage Guidelines".

One of the main questions I still have is, if moisture contributes to delamination by the internal forces generated internally on the PCB when heating up the board at high temperatures due to the evaporation of the water, why would anybody recommend temperatures above 100 °C which is the boiling temp for water? For instance, baking at 125 °C would create the same effects we are trying to avoid, wouldn't it?

Does anybody know any good reading material to learn about this?

Thanks for the help!

Rigo Garcia

Sr. Quality Assurance Engineer
Workmanship Standards, Code 300
NASA, Goddard Space Flight Center
Greenbelt, MD  20771
Phone. (301) 286-6129
Fax.       (301) 286-6576


______________________________________________________________________
This email has been scanned by the Symantec Email Security.cloud service.
For more information please contact helpdesk at x2960 or [log in to unmask]<[log in to unmask]>
______________________________________________________________________

---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 16.0 To unsubscribe, send a message to [log in to unmask]<[log in to unmask]> with following text in the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]<[log in to unmask]>: SET Technet NOMAIL or (MAIL) To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]<[log in to unmask]>: SET Technet Digest Search the archives of previous posts at: http://listserv.ipc.org/archives For additional information, or contact Keach Sasamori at [log in to unmask]<[log in to unmask]> or 847-615-7100 ext.2815
-----------------------------------------------------



______________________________________________________________________
This email has been scanned by the Symantec Email Security.cloud service.
For more information please contact helpdesk at x2960 or [log in to unmask] ______________________________________________________________________

---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 16.0 To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL) To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest Search the archives of previous posts at: http://listserv.ipc.org/archives For additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815
-----------------------------------------------------

______________________________________________________________________
This email has been scanned by the Symantec Email Security.cloud service.
For more information please contact helpdesk at x2960 or [log in to unmask] ______________________________________________________________________

---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 16.0 To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL) To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest Search the archives of previous posts at: http://listserv.ipc.org/archives For additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815
-----------------------------------------------------

______________________________________________________________________
This email has been scanned by the Symantec Email Security.cloud service.
For more information please contact helpdesk at x2960 or [log in to unmask] ______________________________________________________________________

---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 16.0 To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL) To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest Search the archives of previous posts at: http://listserv.ipc.org/archives For additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815
-----------------------------------------------------



______________________________________________________________________
This email has been scanned by the Symantec Email Security.cloud service.
For more information please contact helpdesk at x2960 or [log in to unmask] 
______________________________________________________________________

---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 16.0
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Technet
To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL)
To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest
Search the archives of previous posts at: http://listserv.ipc.org/archives
For additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815
-----------------------------------------------------

ATOM RSS1 RSS2