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March 2014

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Subject:
From:
Nagaraj Shanmugam <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Nagaraj Shanmugam <[log in to unmask]>
Date:
Wed, 19 Mar 2014 04:40:52 -0700
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Thanks for the information and I understand  the reason now , the definition of 'Microvia' ITSELF is getting changed as the technology advances.
I will discuss with our FAB house to have FAB notes updated in their  terminology.

Thanks,
Nagaraj.

From: Ragesh [mailto:[log in to unmask]]
Sent: 14 March 2014 4:44
To: TechNet E-Mail Forum; Nagaraj Shanmugam
Subject: Re: [TN] Via classification in Fabrication world

A recent blog pot in IPC website clarifies the confusion over the definition of Microvia

http://blog.ipc.org/2014/01/10/new-microvia-definition-seeing-broader-usage/

New Microvia Definition Seeing Broader Usage

In 2013, IPC changed its definition of a microvia. Before then, a microvia was defined as any printed board with holes that have a diameter of equal to or less than 0.15 mm [0.006 in]. Over time, that size became common, while more challenging geometries emerged to alter the definition of microvia structures.

IPC decided it was pointless to continue setting strict size parameters that would need to be updated continually.

Now, microvia structures are being defined by the aspect ratio of a hole, which is the ratio of the length or depth of a hole to its preplated diameter. This approach acknowledges that a hole diameter of, say 0.10 mm [0.004 in] will be challenging to adequately plate with copper on a 10-layer board (high aspect ratio), while the same size hole will be comparatively easy to plate if the board has two layers (low aspect ratio) that use the same materials in the 10-layer board.

This definition has until recently been found only in IPC-T-50K, Terms and Definitions for Interconnecting and Packaging Electronic Circuits, published in June 2013. The new definition is now being phased into printed board design and performance standards. IPC-6013C, Qualification and Performance Specification for Flexible Printed Boards, published in December 2013, is the first to cite this definition.

This year, additional standards and handbooks will migrate to the revision. That will make life simpler for companies that want to differentiate microvia capabilities and requirements as technology continues to evolve.

Again its best to talk to your fab house to make sure if they align to the same or not.

-Ragesh.

On 14 March 2014 15:09, Nagaraj Shanmugam <[log in to unmask]<mailto:[log in to unmask]>> wrote:
Experts,

I ran into misunderstanding often on via classification on PCBs  and like to have clear understanding on this forum.
As layout designer I classify vias
        - based on drill depth as Blind via(external to internal), Buried via(with in internal) and through hole via (external to external).
        - based on via stack as Stacked via(Blind/Buried vias placed at same locations) and staggered via (blind/buried via placed apart may have pad overlaps)

I am fine and clear up to hear.

Now, as I discuss with latest technologies /package
        - on tighter pitch BGAs say 0.4mm pitch BGA's the VIP(via in pad) come into role and need via filling.
        - high power ICs with thermal pad which needs thermal vias for heat dissipation, these via need plugging

Here the discussion starts with Fabricator's and lead to misunderstanding on via definitions
- They call  Microvia to plate and shut copper
        What micro via means?
                a) Some refers to  Blind via but with limitation in the depth that the can only go one layer down from external layers with drill size less than 6mils.
                b) some inform they are Via in Pad using blind vias which is of drill size 6mils and less
                c) some refers to any via of drill size less than 6mils and is laser drilled called Microvia and the via doesn't matter blind/buried/through hole
                d) few other says its HDI(- High density interconnect) via and this includes Blind and buried but not through hole via

I am totally lost here - Please help to understand the via terminologies in Fabrication world specifically Microvia.

Thanks in advance for your inputs.

Thanks,
Nagaraj.


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