Juliano, you're right,
for PCB the Sensitivity Level are not available. Too many variables could
influence the M-Sensitivity. I found literature attributing MSL-3 at least.
It could be, but how we are sure about the kind of laminate, amountof
prepreg, % of resin, % of fibreglass or copper, PCB size and thickness,
number of layers, and so on. All PCB/PWB are different among them.
Then establish the MAMC( Maximum Acceptable Moisture Content) acceptable for
those PCB.
Best way to define the MAMC is indicated in the IPC-TM-650 2.6.28 attached
to IPC-1601 ( or downloadable from IPC for free).
Not so easy test to perform if Laminate Witness Coupons ( see IPC-1601 4.2.5
) are not available on your PCB (Panel)
I know, you now are in front a practical problem to solve and not have time
to spend on theories, but that is the right way to understand the technique.
Other points, which kind of packaging is protecting your PCB ? Dray Pack ?
Real Dry Pack ? or simply thermal shrinkable PE or PET with a very weak
material thickness on corner of package ? bottom PE pluryball? etc...
Also, those PCB have to withstand SnPb or Pb Free Reflow temperature ? More
critical situation in case of moisture entrapped in PCB when Pb Free Reflow.
Be careful, by experience, often HIC dos not tell you the real moisture
content inside PCBs. It exist difference in % moisture absorbed, according
to if PCB is on top of pile, inside the middle or bottom of packaging
(pile). By following the TM-650 2.6.28 I discovered interesting moisture
absorption behaviours among PCB packaged inside same pack.
HIC is a good help but some time gives misleading indications, be careful
when interpreting it ( by experience).
Do not forget also there are fake HICs running around.
Check the fabrication Data Code of your PCB, if not so old, don't worry so
much . Just to stay quite, if you have an oven available, do a light bake,
Max 125°C 8h or less. Pile-up the PCB inside the oven max 25 mm tall.
Once bake is completed, leave PCB in the oven until room temperature
(almost) will be reached, then remove and use (reflow) very quickly, as soon
as possible. Remember, no need to totally dry-off the PCB, just keep the
MAMC at the appropriate %, considering also if Pb o PB free reflow
temperature those PCBs have to withstand
If PCB fabrication Data Code is too old, I suggest you to follow TM
650-2.6.28 before to guess if bake need to be done or not. Some time is
better not perform PCB bake then perform it in a wrong way.
etc...
Gabriele
-----Messaggio originale-----
Da: TechNet [mailto:[log in to unmask]] Per conto di Datacom - Juliano Ribeiro
Inviato: mercoledì 30 aprile 2014 22.10
A: [log in to unmask]
Oggetto: [TN] RES: [TN] PCB Humidity
Thank you Gabriele for your answer, but the IPC1601 don't have an
information about what are the maximum level Humidity? Or I didn't find this
information.
For example, the components according to thickness are Level 3 or 4 or....
and the PCB Is there table about this?
We need to register in my incoming to verify the HIC, but what's acceptable
humidity?
Thank you
_____________________________
Juliano Bettim Ribeiro
DATACOM
ENGENHARIA DE PROCESSOS
Rua América Nº 1000 - Eldorado do Sul - RS CEP: 92990-000
+55 (51) 8446-2135
+55 (51) 3933-3000
Ramal: 3877
[log in to unmask]
www.datacom.ind.br
-----Mensagem original-----
De: SALA GABRIELE [mailto:[log in to unmask]]
Enviada em: quarta-feira, 30 de abril de 2014 16:10
Para: 'TechNet E-Mail Forum'; 'Datacom - Juliano Ribeiro'
Assunto: R: [TN] PCB Humidity
Hi Juliano,
this standard gives worthy guidelines:
IPC-1601 Printed Board Handling and Storage Guidelines.
http://www.ipc.org/TOC/IPC-1601.pdf
Gabriele
-----Messaggio originale-----
Da: TechNet [mailto:[log in to unmask]] Per conto di Datacom - Juliano Ribeiro
Inviato: mercoledì 30 aprile 2014 19.57
A: [log in to unmask]
Oggetto: [TN] PCB Humidity
Hi to all,
We received a PCB lot with HIC more than 10% but less than 60%.
What is IPC/JEDEC or others specifications to Humidity limits to PCB?
Is it good or no good PCB?
Thank you
_____________________________
Juliano Bettim Ribeiro
DATACOM
ENGENHARIA DE PROCESSOS
Rua América Nº 1000 - Eldorado do Sul - RS CEP: 92990-000
+55 (51) 8446-2135
+55 (51) 3933-3000
Ramal: 3877
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