I will be interested to read the replies of others. 
We've never probed microvias but as vias in general are probably the
least reliable part of a pcb and pcbs often the least reliable part of
an assembly.............do you want to be "hitting it with a LOT of
force"????
Our approach is to avoid probe testing on vias, never yet contemplated a
microvia.
Rex

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Valerie St.Cyr
Sent: 19 April 2006 15:10
To: [log in to unmask]
Subject: [TN] Question re Test Probe and blind microvia

All,

I have a question: have any of you first hand experience with allowing
blind microvias to be used as test points for In-circuit or Functional
Test?

The Engineer would like to probe a microvia to eliminate the stub we
would normally have from a through hole via used as a test point. I
don't know if that should be avoided. The probes we used are either
"spear" or "blade" tips; I am talking about probing the loaded board, so
this means probing after the board has seen 3 or maybe 4 reflows; the
microvia starting laser ablated diameter is typically .006"; if it is a
Layer 1 to Layer 2 it is .003" or .004" deep (we used prepreg in that
opening, no RCC); if it is Layer 1 to Layer 3, the depth could increase
by anywhere from another .0035" to .0055"ish.

Our plating specification is IPC6012A Class 3. Our intention would be to
drop that blind via in a very large pad, much larger than normal for a
blind via; then paste it so it is closed up when we go to probe. That
will keep the probe from directly piercing the sidewall plating or the
hole knee. Which leaves, I think, the question of how well the plated
copper is adhered to the copper foil capture pad - we will be hitting it
with a LOT of force - will that mechanical stress cause a de-bonding or
weaken that bond ? What if the board needs to be retested and retested
if there is a fault and we have to do repetitive debug?

So, anyone with experience probing to microvias, your  knowledge would
help us a lot.

Thank you,


---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 1.8e To
unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt or
(re-start) delivery of Technet send e-mail to [log in to unmask]: SET
Technet NOMAIL or (MAIL) To receive ONE mailing per day of all the
posts: send e-mail to [log in to unmask]: SET Technet Digest Search the
archives of previous posts at: http://listserv.ipc.org/archives Please
visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for
additional information, or contact Keach Sasamori at [log in to unmask] or
847-615-7100 ext.2815
-----------------------------------------------------
Valerie

________________________________________________________________________
This email has been scanned for all viruses by the MessageLabs SkyScan
service.
________________________________________________________________________



This email has been scanned for all known viruses by the
MessageLabs SkyScan service.
================================================================
This email (including any attachments) is confidential and/or may be legally privileged.  It is intended for the named recipient (s) only and may not be forwarded, disclosed or otherwise disseminated 

Although this email has been scanned for viruses, WE DO NOT (to the extent permitted by law) ACCEPT ANY LIABILITY WHATSOEVER for any virus infection, compromise of security or losses resulting from vi

NO CONTRACT MAY BE FORMED OR DOCUMENTS SERVED BY THIS EMAIL unless specifically agreed to in writing and signed by a Director of Hansatech.  Any views or opinions expressed in this email are those of 

If you have received this email in error please contact the IT department immediately on  (01202) 674 333 or (01553) 691 022 prior to deletion.
================================================================

---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 1.8e
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Technet
To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL)
To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest
Search the archives of previous posts at: http://listserv.ipc.org/archives
Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815
-----------------------------------------------------