Printed Circuit Board Assembly & PCB Design SMT Electronics Assembly Manufacturing Forum

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


MSL

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#75985

MSL | 13 July, 2016

How the moisture is not effecting the moisture sensitive devices after board assembly solder process when kept inside a cabinet with IP 20 rated?

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#75987

MSL | 13 July, 2016

Moisture before reflow is consideration, because damages parts and boards in the reflow process. It is all about this water expanding as gas and cracks part or causes PCB delamination. Moisture after reflow is still affecting the work of the product. For that reason we do conformal coating, potting and other encapsulating processes.

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#75989

MSL | 13 July, 2016

From "Assembly" magazine, "Moisture-Sensitive Devices" [ http://www.assemblymag.com/articles/85082-moisture-sensitive-devices ] ... a description of the moisture sensitive device problem.

I agree with Evtimov

* During board assembly solder process, your designers expect the assembly to reach temperatures that may cause component damage

* When kept inside a cabinet with IP 20, your designers don't expect the assembly to reach temperatures that would cause component damage

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#75990

MSL | 14 July, 2016

Thanks Evtimav and davef...

We are doing tar potting only over the moisture sensitive device (not all over the PCB) to make sure that it does not get effected by moisture. But am unable to test the reliability of the process. Continuous switching or life test is not giving the desired result.

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#75993

MSL | 14 July, 2016

Here is some more information: "Moisture can increase the dielectric constant, leading to changes in impedance, switching speeds and propagation delay times. "

I am not sure if you can accurately measure any of these on your assembly but it looks like it might affect the timing work of your device.

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#76000

MSL | 15 July, 2016

Thanks for the suggestions..will ask my RnD team to introduce such procedures which can replicate the points you have mentioned.

We have initiated to implement the MSD devices proper handling in our factory premises so that field rejections which are related to this can be eliminated.

As mentioned in the forum, to locate the rejection cause is due to moisture is a difficult task.So we are including the MSL precautions in our process.

Some standards mention to solder the MSD within 4 hours from the time it is removed from spool. But this is something which is a bit difficult to follow.Is there any other alternative to this?

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#76001

MSL | 15 July, 2016

You always follow the MSL label(I attached the table). 1. Use parts 2. Reseal the parts that left. If exparation date is getting close: 1. Use parts 2. Bake the parts left 3. Reseal

Attachments:

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#76002

MSL | 15 July, 2016

This conversation is making my head hurt. Before your engineers respin the design, some basic questions need answers.

* How do you know that the field failures were caused by MSD damage?

* What is going on in the field that is causing these failures?

* How do you know that the field failures are caused by continuous switching or life test?

* How do you know that the field failures are caused by tar sealing process?

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#76525

MSL | 2 November, 2016

The moisture before re flow can be considered since it may cause damage to boards. Anyway Thanks for your suggestions and it has just been cleared with my team. But currently they are busy with the work in top rated essay writing service http://best-essay-writing-service-reviews.com/

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