Hey Bhanu, in my previous life we always discouraged etchback/3 pt. Legacy users/designs wouldn’t relent even in the face of reduced CITC performance (sometimes vastly reduced), when compared side to side under controlled conditions (same boards with and without 3pt). Kevin Knadle has all sorts of data showing this, unsure if he’s published anything or kept it under wraps.... Basically plasma etchback creates gauges or amplifies existing drill gauges in order to create the 3pt. Plating those tight without plated copper pinch points becomes tricky, and you know the rest. You may be able to pin Kevin down during the May IPC seminar in MD.... Give me a call if you want to discuss further.



Sent from my iPhone



> On Apr 26, 2018, at 9:56 AM, Bhanu Sood <[log in to unmask]> wrote:

> 

> Good morning,

> 

> Is there a recent peer reviewed study or presentation (reported in open

> literature) that discusses the relative reliability of various etchback

> conditions in context of applied stresses, processing conditions and

> materials (high Tg 180C++ laminates, higher 10%++ elongation foil and

> higher 15%++ elongation plating chemistries)? (I am not looking for

> sections/paragraphs of applicable Standards)

> 

> In some instances, the merits of positive etchback are discussed in context

> of a "three point connection", but one disadvantage of this arrangement is

> poor low cycle fatigue reliability.

> Literature has reported that negative etchback "up to a certain extent" is

> reliable, however one disadvantage is a possibly poor foil to barrel

> connection in cases where process residues prevent a good connection with

> the foil. The no etchback (only smear removed) is also shown in literature

> as reliable, and the middle of the road solution to the etchback

> requirement.

> 

> Thanks,

> Bhanu

> 

> -- 

> Bhanu Sood