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FR4 time*temperature discoloration

J

John S

Jan 1, 1970
0
A component hot enough will cause FR4 to discolor after a few years. An
end user will suspect there is a problem with the board (even if there
is none) because of the discoloration.

Does anybody know how hot a component on the board can be and still not
cause discoloration eventually?

I have searched, but I only found information regarding short-term
temperature extremes.

Thanks.

John S
 
M

Maynard A. Philbrook Jr.

Jan 1, 1970
0
A component hot enough will cause FR4 to discolor after a few years. An
end user will suspect there is a problem with the board (even if there
is none) because of the discoloration.

Does anybody know how hot a component on the board can be and still not
cause discoloration eventually?

I have searched, but I only found information regarding short-term
temperature extremes.

Thanks.

John S

If you are concern, there is also FR5 to use. that is a higher
temperature material and also higher voltage handling.

P.S.
It does cost more, obviously..

Jamie
 
P

Phil Hobbs

Jan 1, 1970
0
A component hot enough will cause FR4 to discolor after a few years. An
end user will suspect there is a problem with the board (even if there
is none) because of the discoloration.

Does anybody know how hot a component on the board can be and still not
cause discoloration eventually?

I have searched, but I only found information regarding short-term
temperature extremes.

Thanks.

John S

Use black solder mask.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net
 
J

John S

Jan 1, 1970
0
Use black solder mask.

Cheers

Phil Hobbs

A good way of hiding it, but what if forced to use the typical green color?

Cheers,
John S
 
L

Lasse Langwadt Christensen

Jan 1, 1970
0
Den søndag den 22. december 2013 23.41.16 UTC+1 skrev John S:
A good way of hiding it, but what if forced to use the typical green color?



Cheers,

John S

remove the solder mask underneath the hot part?

-Lasse
 
K

Kevin McMurtrie

Jan 1, 1970
0
John S <[email protected]> said:
A component hot enough will cause FR4 to discolor after a few years. An
end user will suspect there is a problem with the board (even if there
is none) because of the discoloration.

Does anybody know how hot a component on the board can be and still not
cause discoloration eventually?

I have searched, but I only found information regarding short-term
temperature extremes.

Thanks.

John S

My experience is that solder ages slightly faster than FR4, and copper
traces age almost as fast. Your customers are likely right to call
boards defective when they have dark spots.

It was common in 1980s home theater systems to have extremely hot
voltage regulator transistors that eventually destroyed their solder
joints. You could probably find one and measure the temperature. I'd
guess nearly 200C based on what they do to your finger tip.
 
K

Klaus Kragelund

Jan 1, 1970
0
A component hot enough will cause FR4 to discolor after a few years. An

end user will suspect there is a problem with the board (even if there

is none) because of the discoloration.



Does anybody know how hot a component on the board can be and still not

cause discoloration eventually?



I have searched, but I only found information regarding short-term

temperature extremes.

I looked into this some years ago. The only information I could find was submitted by Isola, referring to UL746 which has figures for the lifetime versus temperature:

https://www.dropbox.com/s/oyfnhv9fhk9iq3d/1275_001.pdf

It does not however state the point at which the discoleration occurs

The rule we used for FR4 temperatue was max 95 degrees, which would be on the conservative IMHO.

Regards

Klaus
 
J

John S

Jan 1, 1970
0
I looked into this some years ago. The only information I could find was submitted by Isola, referring to UL746 which has figures for the lifetime versus temperature:

https://www.dropbox.com/s/oyfnhv9fhk9iq3d/1275_001.pdf

It does not however state the point at which the discoleration occurs

The rule we used for FR4 temperatue was max 95 degrees, which would be on the conservative IMHO.

Regards

Klaus

Many thanks. This is a number to keep in mind. Every degree lower is
better, I know.

Cheers,
John
 
J

John S

Jan 1, 1970
0
A component hot enough will cause FR4 to discolor after a few years. An
end user will suspect there is a problem with the board (even if there
is none) because of the discoloration.

Does anybody know how hot a component on the board can be and still not
cause discoloration eventually?

I have searched, but I only found information regarding short-term
temperature extremes.

Thanks.

John S

Thanks to all who contributed. I think I have a goal now.

Merry Christmas.

John S
 
L

Lasse Langwadt Christensen

Jan 1, 1970
0
Den mandag den 23. december 2013 09.26.20 UTC+1 skrev Klaus Kragelund:
I looked into this some years ago. The only information I could find was submitted by Isola, referring to UL746 which has figures for the lifetime versus temperature:



https://www.dropbox.com/s/oyfnhv9fhk9iq3d/1275_001.pdf



It does not however state the point at which the discoleration occurs



The rule we used for FR4 temperatue was max 95 degrees, which would be on the conservative IMHO.



Regards



Klaus

there is something about the resin if FR4 starting to change state at
~130C causing a big expansion in the Z direction stressing vias etc.

-Lasse
 
S

Spehro Pefhany

Jan 1, 1970
0
there is something about the resin if FR4 starting to change state at
~130C causing a big expansion in the Z direction stressing vias etc.

-Lasse

The glass transition temperature (Tg) of FR4 is 130°C, give or take
10°C or so. Indeed, it's like a phase change.

The expansion of the resin would be the same in all directions, except
the glass fibers limit the dimensional change in the X & Y directions
due to the layup.

One rule of thumb to prevent delamination is to keep the operation
temperature of the laminate at least 25°C below the Tg.

You can specify materials with a Tg of 170°C or even higher (for a
premium, of course).


Best regards,
Spehro Pefhany
 
J

John S

Jan 1, 1970
0
So: I don't know the answer for this, but reading Kevin's comment about
high temperatures accelerating the breakdown of solder made me think.

There's probably a MIL- handbook out there, possibly with the words
"reliability" and "electronic" in its title, that addresses all of this.
Maybe this would help narrow your search enough that you'll find an
answer?

I know that there are pretty firm rules for computing the reliability of
a PCB given various parameters: I used to work at a place where one of
the steps in the design process was to give the schematics and PCB
layouts to Leo (uh -- per ISO 9000 that's "the reliability guy", but we
all said "Leo"). Leo would then withdraw into his cubicle for a period
of time marked by odd-scented smoke, purple lightning, and strange cries,
after which we'd get a completed reliability estimate. The janitorial
staff would clean up the chicken entrails later.

Wow! Thanks. Best info yet! First I need to find a chicken. Then I need
to find out if my cleaning lady understands to clean up what's left
after... er, what do I do with the chicken?

I'm sure that the standard that he was working from in such a scientific
manner included how to treat hot components, and I'm sure that you could
work backwards from that to how to reduce the heating from same.

Heating a chicken is no problem. There are a number of ways. But, don't
tell the ASPCA.
 
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