The video clips are on my sever to access them now
use the following links. You will need RealPlayer to view the
clips.
I produced the video clips for a flip chip and
underfill workshop I was organising with Speedline Technologies in the UK at the
start of the year. I was trying to show the problems of outgassing from the mask
during reflow of no-flow underfills. The same issue can occur with traditional
underfill but these can cause misaligment of the devices before the solder joint
is formed on the connection pads.
I am currently conducting a project as part of team
at NPL on solder mask related problems related to cure of masks.
The text below outlines the project and I have also
used it for a abstract for the Printed Circuit Board World
Convention.
Hope this all of interest.
Characterising Solder Resist/Mask Performance
and Degree of Cure
Chris Hunt, Alan Brewing and Bob Willis
National Physical Laboratory Teddington, Middlesex, England
Industry currently uses a number of simple ad-hoc
evaluation test methods that correlate poorly with the mask performance during
assembly. The industry has long understood that the test methods contained in
national and international specifications to be inadequate. NPL is to evaluate a
number of test methods and show the relevance to issues experienced during
assembly operations. The project will also bench-mark the current test methods
with new procedures.
Issues with voiding during underfill cure have been
documented, where out-gassing from the solder mask has occurred. Voids in the
underfill can dramatically impact on the reliability performance of the solder
joints and the mechanical strength of devices to the resist surface. This is
particularly important with modern electronics. Evolution of gas and changes in
surface tension can significantly influence the occurrence, or the adhesion of
solder balls, during soldering. Absorption by solder masks of solvents and other
components from cleaning, which then can be desorbed, will significantly impinge
on solder wetting.
The aim of the NPL project in conjunction to
leading solder mask supplier and soldering material manufacturers will help to
achieve the following project goals:
Produce a code of practice to define test methods
and criteria to allow companies to simply define and test printed circuit boards
prior to assembly or supply.
Investigate current and new methods of assessing
the degree of cure of solder masks after fabrication and prior to
assembly. Define test methods which could be economically introduced to
assembly and fabrication operations.
Compare assembly defects like resist out-gassing,
underfill voiding and solder balling and the variations on selected solder
resist surfaces.
Propose these test methods and procedures to
national and international standards committees to incorporate into future
standards to reduce the variation of test results in the industry.
This technical paper will outline the work
conducted and the results obtained.
Bob Willis
Electronic Presentation Services
2 Fourth Ave, Chelmsford,
Essex, CM1 4HA England
----- Original Message -----
Sent: Tuesday, November 20, 2001 3:40
PM
Subject: Solder mask outgassing
Bob,
I for one am interested in seeing the RealTime
video clip/s on solder mask
outgassing
Steven Creswick - Gentex
Corp