TECHNET Archives

July 2008

TechNet@IPC.ORG

Options: Use Monospaced Font
Show Text Part by Default
Show All Mail Headers

Message: [<< First] [< Prev] [Next >] [Last >>]
Topic: [<< First] [< Prev] [Next >] [Last >>]
Author: [<< First] [< Prev] [Next >] [Last >>]

Print Reply
Subject:
From:
Werner Engelmaier /* <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, [log in to unmask]
Date:
Sat, 5 Jul 2008 09:57:02 EDT
Content-Type:
text/plain
Parts/Attachments:
text/plain (65 lines)
Wow Jan,
You have: "PCBs approx 450mm long, 50mm wide, 1.7mm thick, 12 layers, 17u 
copper inner
layers, Isola IS420 material, boards are produced with longest dimension in 
warp direction in PCB production panel" —and you expect a 75um tolerance after 
subjecting the PCB to board drying and leadfree reflow.

Just consider that in PCBs you are marrying 4 different materials [laminate, 
prepreg, woven glass-fiber reinforcement, copper] together all of whom have 
significantly different physical properties, particularly at different T's and 
in different directions.

The laminate (which is fully cured) and the prepreg (not fully cured) have 
different resin contents, go through glass transition (which changes molecular 
structure and is not fully reversible, only nearly so), start to decompose at 
SAC solder T's (actual weight loss, which is irreversible).

The glass-cloths is in your PCBs laid up with the warp direction in the 
longest dimension in the PCB production panel making your PCBs quite non-uniform in 
the x and y directions [the normal practice is to alternate warp and fill 
directions on alternate layers to equalize the different properties in the warp 
and fill directions—even with that, it is not uncommon to measure CTE-values 
different in x and y by as much as 2 ppm/C].

The copper layers are mostly etched   away in irregular [in the sense of 
physical behavior] patterns.

—and you expect a 75um tolerance after subjecting the PCB to board drying and 
leadfree reflow?!



Werner
Future workshops:
Pb-Free Soldering Processes—Survival, Quality, Reliability, July 17/18, Thal, 
Switzerland
Pb-Free Soldering Processes—Survival, Quality, Reliability, July 21/22, Bad 
Segeberg, Germany
Pb-Free Soldering Processes—Survival, Quality, Reliability, August 18, O
rlando
Reliability Issues with Lead-Free Soldering Processes, September 22, 
Schaumburg
Failure Mode and Root Cause Analyses Reliability (Fatigue, Brittle Fracture, 
ENIG), September 22, Schaumburg
Solder Joint Reliability: Parts 1 & 4, Oct. 9, Moscow, Russia
Solder Joint Reliability: Parts 1 & 4, Oct. 17, Timisoara, Rumania
Solder Joint Reliability: Parts 1 & 4, Oct. 22, Tallinn, Estonia



**************
Gas prices getting you down? Search AOL Autos for 
fuel-efficient used cars.
      (http://autos.aol.com/used?ncid=aolaut00050000000007)

---------------------------------------------------
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
-----------------------------------------------------

ATOM RSS1 RSS2