Date: Sun, 9 Dec 2001
00:00:11 -0600
Subject: TechNet Digest - 7 Dec 2001 to 8 Dec 2001
(#2001-766)
There are 2 messages totalling 54 lines in this issue.
Topics of the day:
1. BGA Rework Equipment
2. Plating and Resin Recession
---------------------------------------------------------------------------------
Technet Mail List provided as a free service by IPC using LISTSERV
1.8d
the BODY (NOT the subject field): SIGNOFF Technet
To temporarily halt delivery of Technet send the following message:
SET Technet NOMAIL
Search previous postings at:
www.ipc.org > On-Line
Resources & Databases > E-mail Archives
---------------------------------------------------------------------------------
Date: Sat, 8 Dec 2001 05:23:36 -0600
Subject: Re: BGA Rework Equipment
I really echo Warren's message. When first developing HP's BGA
rework
process, using SRT, it took three months to get everything almost
right.
Then, there were surprises needing rectification. It never really
ended as
new boards and components were designed and built plus CPI.
The process first must be developed. It must be transferred to
manufacturing
including all procedures for everyone and all parts involved, or
those
perceived to be, it must be validated for each part on each board
type, and
operators must be trained for each shift. Though most all operators
great at
their jobs, some definitely caught on quicker and did consistently
better
jobs than others.
Profiles alone can take much development time, and they're long
themselves,
no matter the paste or original assembly profile. Parts must be
removed and
sites cleaned and touched up and thoroughly inspected. A costly
supply of
nozzles must be bought as well. Micro stencils must be purchased
and
processes developed for their use. Part replacement and reflow
processes
must be right on. X-ray inspection is a must for rework, as it is
for
prototypes, before final test, and on it goes.
This is a good one to "farm out." I think you already knew
this or are an
excellent rework engineer yourself.
MoonMan
Date: Sat, 8 Dec 2001 17:45:23 EST
Subject: Re: Plating and Resin Recession
MIME-Version: 1.0
Content-Type: text/plain; charset="US-ASCII"
Content-Transfer-Encoding: 7bit
Hi Roger,
Thicker copper deposits have indeed greater (but not better)
elongation
values than thinner deposits. This, however, does not mean that
thinner
deposits have less ductility; the lower elongation value is an
artifact of
using a test method which is inappropriate for sample geometries
like plated
copper foils. Elongation tests work well for specimen for circular
and square
cross-section; foil specimen have a cross-sectional aspect ratio of
500 to
1000, which creates this type of artifact.
This is the reason test methods specific for foils (ASTM E 796
"Standard Test
Method for Ductility Testing of Metallic Foil," IPC-TM-650, TM
2.4.2.1
"Flexural Fatigue and Ductility, Foil" ) were developed.
These test methods
show there is no difference in ductility for thin or thick foils
from the
same batch.