LMG1205: Do I need an underfill or not?

Klemens Dösinger

Part Number: LMG1205
Other Parts Discussed in Thread: UCC27712

Hi, let's look at the following example using the LMG1205YFXT:

I have 5V between VDD and VSS and there are 80V between HS and VSS -> 75V between HS and VDD

These two pins are neighbours and IPC-2221B requires a clearance between the ball surface greater than 0.5mm. However the BGA pitch is 0.4mm, which means that the balls will have a clearance of ~0.2mm.

If there is a polymer coating of any kind, the requirement is only 0.13mm, so I conclude that the BGA package requires an underfill or a conformal coating to be used. I just want to know if that is the case or if I overlooked something.

So, do I need the coating to fulfill the requirements given in PCB and safety standards like the IPC-2221B or the IEC62368-1?

Thanks for your help

over 1 year ago

0 Alexander Mazany over 1 year ago

TI__Genius 11770 points

Hi Klemens,

It may be necessary to use a conformal coating to meet the IPC/IEC standards at this voltage. I'm not sure exactly how this rule applies to BGA packages where the pins are mostly encased by the package, which I think should reduce any possible pollution.

Ultimately, it is up to the customer to meet these standards for their system. So while I think your reasoning makes sense, I can't say for certain what is and isn't required to meet those standards. I am aware of similar cases with UCC27712 where customers have added coatings to meet IEC standards.

Thanks,

Alex M.

0 Klemens Dösinger over 1 year ago in reply to Alexander Mazany

Prodigy 30 points

Hi Alex,

I am a bit surprised about the lack of information about this topic. I thought that everyone assembling BGA packages with operating voltages over 50V must come across this. Therefore I was surprised that TI itself didn't give me an answer but instead suggested posting it in the forum. So thanks for your answer but this doesn't really help me. Is there anyone with experience using BGAs?

+1 Alexander Mazany over 1 year ago in reply to Klemens Dösinger

TI__Genius 11770 points

Hi Klemens,

I asked our packaging expert about this subject. He mentioned that underfills are commonly used in parts like this to help meet these standards. I found one other thread where this came up also:

https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/937965/lmg1205-is-underfill-recommended-for-this-device

Hopefully this is more helpful.

Thanks,

Alex M.

0 Alexander Mazany over 1 year ago in reply to Alexander Mazany

TI__Genius 11770 points

Hi Klemens,

Let me rephrase this.

To meet these IEC and IPC standards using this part and these operating conditions, an underfill will be required.

Thanks,

Alex M.

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LMG1205: Do I need an underfill or not?