ED stands for "electro-deposited" and they were most likely talking about 
electrophoretic photoresist.  ED photoresists are deposited onto a (usually) 
copper surface using an electric current, much like electroplating.  There 
are both anodic and cathodic systems (where the copper surface acts as 
either the anode or cathode), and both positive-acting and negative-acting 
(imaging) formulations.

An advantage to these types of resists is the ability to conformally coat 
all of the copper surfaces, including hole walls and other 3-dimensional 
features.  The resists are generally coated to a thickness of 0.2-0.3 mils 
(after drying), so it is clear that very fine feature definition is 
possible.  The best applications appear to be 1) very fine feature 
innerlayers with vias, 2) as a final etch resist after panel copper plate, 
and 3) on 3-D circuit boards, and 4) other, probably non-PWB applications. 
 On the other hand, these resists are not suitable for full copper plating, 
as the copper would overplate over the thin resist.

While it is true that ED resists have had some failures, there have also 
been success stories, and there is new technology available that works very 
well.  The most interest in the market place has been for a positive-acting 
system, because small vias can be coated but do not need to be imaged in 
order to remain protected during subsequent etching (or plating) steps. 
 This eliminates the concern of getting enough UV energy in high aspect 
ratio holes to insure cross-linking (hardening) of the resist, since 
positive resists are already cross-linked and "un-crosslink" during UV 
exposure.

I hope this helps your understanding.

Patty Goldman
PPG Industries, Inc.
(yes, we supply this type of photoresist)
 ----------
From: yuanl
To: TechNet
Subject: What is ED?
Date: Friday, May 30, 1997 11:50AM



  Sometime ago, a PCB manufacturer gave a presentation and talked about "ED" 

  technology while unfortunately I was not present. People in the
  presentation are still not clear what ED is and asked for my help. I am 
not
  a PCB expert either. I tried to find something on the net w/o luck.

  Is ED a new resist technology? What are the conventional technologies?
  Could someone on the net offer some insights or some references?

  Yuan Li
  Exabyte

***************************************************************************
* TechNet mail list is provided as a service by IPC using SmartList v3.05 *
***************************************************************************
* To subscribe/unsubscribe send a message <to: [log in to unmask]>   *
* with <subject: subscribe/unsubscribe> and no text in the body.          *
***************************************************************************
* If you are having a problem with the IPC TechNet forum please contact   *
* Dmitriy Sklyar at 847-509-9700 ext. 311 or email at [log in to unmask]      *
***************************************************************************


***************************************************************************
* TechNet mail list is provided as a service by IPC using SmartList v3.05 *
***************************************************************************
* To subscribe/unsubscribe send a message <to: [log in to unmask]>   *
* with <subject: subscribe/unsubscribe> and no text in the body.          *
***************************************************************************
* If you are having a problem with the IPC TechNet forum please contact   *
* Dmitriy Sklyar at 847-509-9700 ext. 311 or email at [log in to unmask]      *
***************************************************************************