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Do you need to bake after parts are in the Dry Cabinet

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james

#39322

Do you need to bake after parts are in the Dry Cabinet | 26 January, 2006

Just wondering what others are doing as far MSD parts. We keep most of our parts in the dry cabinet before use. Most bags are openend and have passed the recomendation as far as mounting within a certain time. We have had defects with boards that went to test failed then sent to the oven at 150 d eg F for 2 hours and then passed test. I am assuming the parts have moisture problems. Any suggestions are helpful.

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GS

#39329

Do you need to bake after parts are in the Dry Cabinet | 26 January, 2006

How is RH% inside your Dry Cabinet ?

What is the most critical MDL of your MSDs soldered on your board ?

Best instructions about Handling of MSD you can get from Standard J-STD-033B/C.

The defects you encountered at test it could be moisture absorbed by MSD or PCB as well or humidity under low gap components (BGA, micro BGA, fine pitch components, etc).

Are your board assembled by No Clean Process or Clean Process. In case of Clean process you could get water or cleaning media residuals entrapped under low gap components, etc , as above so by doing bake before test can help.

just my 0,01 $

Best Regards ...........GS

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james

#39382

Do you need to bake after parts are in the Dry Cabinet | 30 January, 2006

We are running under 5% RH. The parts we are having problems with are QFP 208. We have a clean process and right now I am baking 3 boards before they remove the parts and then sending them back to test.

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GS

#39384

Do you need to bake after parts are in the Dry Cabinet | 30 January, 2006

Hi James, it could be the problem is due to residual of cleaner media entrapped under low gap of QFP 208 and 0,5 mm lead pitch.

I remember in the past we had random problems of failure at test after board wash off process (DI Water wash). We met problems on a TBGA 1.00 mm ball pitch, and also with a VHDM Connector on another kind of board.

Due to not enough efficiency of wash machine dryers, water residual use to remain entrapped under component body (TBGA) or inside WHDM connector's housing . Once we discovered the cause of faults at test, we implemented a procedure ( as a process step once boards have got out from washing machine conveyor) to blast boards with dry compressed air (35 PSI max) for few seconds just under the TBGA body side, or contact housing of VHDM connectors.

Following process step was to put all the boards inside an oven at 90�C for at least 30 minutes.It was enough to solve the problem totally.

This was just my experience.

Best regards........GS

PS: TBGA was a MSL-4, correctly handled according to J-STD-033A, but as for above the problem we met was not due to moisture absorbed by component body but due to washing process.

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Mike

#39443

Do you need to bake after parts are in the Dry Cabinet | 1 February, 2006

James, If you have a true MSD issue, then baking them AFTER your reflow is not going to fix the issue. I would have to agree with GS and look at trapped cleaner media (if your not No-clean) under the components, or inside connectors. If your running a no-clean process, then you have another issue. Typically, a MSD sensitive part that has taken in moisture will fail after its first trip into reflow temps. And in my experience , it�s a fatal failure when it happens.

Mike

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Ajay SHarma India

#39568

Backing of Cards | 8 February, 2006

Sir i have a question on Backing of Cards. pls. clarify me that Why we always do backing of cards(90 dC for 1hr. in a Oven) for the reflow process before printing the solder paste on the board. and same for the Curing process we are not backing the PCBs before Glue dispensing,Why? why only reflow soldering required some special conditions and not curing.? pls. explain. thanks. Ajay sharma

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GS

#39570

Backing of Cards | 8 February, 2006

Hi,

just my comments:

Q1) Why we always do backing of cards(90 dC for 1hr. in a Oven) for the re flow process before printing the solder paste on the board to bake

A1) To backe PCB before print and reflow is not a common practice. But probably you have the right technical justification to do it.

Q2) same for the Curing process we are not backing the PCBs before Glue dispensing,Why? why only reflow soldering required some special conditions and not curing.? pls. explain.

A1) The purpose to backe cards (PCB or PBA or MSD as well)is to remove moisture entrapped internally. If moisture remains inside, when PCB is exposed to temperature (>100�C) the moisture changes in vapour/gas generating an internal pressure causing in the worst case damages like internal planes delamination, popcorn effects, degassing, ecc. So you can understand why before reflow it could be necessary to backe and not when you do adhesive curing. The reason is that temperature and PCB exposition to Temperature in Reflow is higher ( 230�C-240�C on hottest PCB point, even higher in case of Lead Free reflow)compared to adhesive Temperature Curing. Remember, highest is the temperature highest are the risks for damages in case of entrapped moisture inside PCB. Curing temperature (in-line oven max 150�C for 2-3 minutes according to the kind of adhesive used) is not a risky situation.

Regards..............GS

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