Subject: | |
From: | |
Reply To: | |
Date: | Mon, 2 Jun 2008 16:23:33 EDT |
Content-Type: | text/plain |
Parts/Attachments: |
|
|
In a message dated 6/2/2008 3:58:59 P.M. Eastern Daylight Time,
[log in to unmask] writes:
KEVIN: Specifically, is it possible, impossible, or just difficult to apply
finish plating to blind and/or soldermask tented vias?
BOB: Possible but difficult for blind vias, no problem for tented. Blind
vias can be plagued by air entrapment. An air bubble in blind via keeps the
finish solution out. For tented vias, simply do the surface finish prior to
tenting.
KEVIN: What are the negatives to tenting both sides of a via vs just one
side? We have PCBs with .015" dia vias. The vias are tented on one side
w/soldermask. The other side terminates as via-in-pad. Finish is ImAg.
BOB: When you tent both sides of a via you create a drum-effect. When the
via subsequently goes through a thermal excursion (Fab House HASL or Assembly
House Reflow) the air in the via rapidly expands, sometimes to the point of
blowing a tent. That frees solder mask fragments onto your assembly (or into
your assembly environment) and makes the via vulnerable to entrapment of
contamination (we used to call them "flux buckets").
KEVIN: Should these vias also exhibit ImAg or be exempt from it due to the
tenting?
BOB: Good question. Exposed copper is never a good idea. But immersion
silver is not intended to be a final finish. Ask any supplier of immersion silver
what the post-assembly service life of immersion silver is, and they'll
likely reply that it's only rated as an interim solderable protectorate (prior to
assembly). PCB finishes that are good for before-and-after assembly
protection include HASL (Sn/Pb and Pb-Free) and ENIG. As for anything else being used
as a final finish (e.g., ImSn, ImAg, OSP) ask before you assume to avoid
disappointment.
ROBERT LAZZARA
VP, Marketing & Tech Support
Atlanta Office: GMT -5
Tel: 800.560.9457 ext. 1
Fax: 800.878.5566
Fax: +1 603.880.7975
Cell: +1 706.498.9138
**************Get trade secrets for amazing burgers. Watch "Cooking with
Tyler Florence" on AOL Food.
(http://food.aol.com/tyler-florence?video=4?&NCID=aolfod00030000000002)
---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 15.0
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
-----------------------------------------------------
|
|
|