Hi, Juliano
I would suggest you start by reading through IPC-1601. It not only describes methods of protection for moisture ingression from cradle to reflow, but also methods of determining how to measure the absorption (adsorption) rates of different types of PWB materials to determine both the time required for bake-out to reach a moisture content of less that 20% of saturated weight, but also the time before the laminate has re-absorbed a moisture content above the 20% level of maximum saturation (from humidity), which is the level of moisture that "usually" can lead to delamination during reflow.

For example, you can diligently follow good baking practices at the PWB vendor, followed by immediate drypak with desiccant, proper handling and storage in the CEM or EMS factory, proper bake before assembly, etc., but did you know that nearly all FR-4 types listed in IPC-4101 can reabsorb at least 50% of their saturated moisture content within just two hours at 70%RH? 
My point is that unless you know (for sure) exactly what the condition of the PWBs is prior to assembly and soldering, and you know just what the rate of moisture ingression is for that particular PWB type, if the boards are allowed to sit out at 50% RH overnight between side two reflow and side one reflow, they could delaminate.

But if you DO know by performing a moisture bake-out study per IPC 1601, and you DO know the rate of re-absorption in a controlled humidity environment, you WILL be able to exclude your own handling and reflow methods as the culprit. 

That leads to using other methods to determine the reason for delamination, and of those there are many, including design stackup, prepreg adhesive skips between layers, etc. These are typically determined by microsectioning through the delaminated areas.

dean

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From: TechNet <[log in to unmask]> On Behalf Of Datacom - Juliano Ribeiro
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Subject: [TN] PCBA Delamination

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Hello to all

 

We have problems with delamination in our PCBA and we would like to test to discover the root cause.

What are the suggestions about test to discover the root cause? The goal is to discover if the root cause is internal or it is supplier.

 

I saw in the IPC600 and found IPC-TM-650 2.4.28.1, does anyone know this test and if that test finds the root cause?

 

In particular we could send the images about problems

 

Thank you a lot

 

Juliano Bettim Ribeiro

DATACOM

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