With regard to cleaning under BGA it is not difficult, the drying stage needs to
be considered but it againg not any more difficult that the existing QFP as the
standoff height is in fact higher. Here are some extracts from the SMART Group
report on BGA. 
The SMART Group also has a video tape showing cleaning trails on BGA, a X-ray
inspection video guide and poster sets which you can get from the SMTA office
contact Tel:612 926 1819  Fax: 612 920 7682 your contact is JoAnn Stromberg.

Introduction to BGA Technology
Duration: 55 minutes 

Component types
Design requirements
Screen print and reflow process
Inspection and quality control
Rework and repair
Process problems and solutions

Introduction to X-Ray Inspection
of BGA and Fine Pitch Joints
Duration: 35 minutes 

Criteria for:  	
component placement
BGA joints
chip components
 J-leads
 gull wing terminations
Common SMT soldering defects
Test sheets for operator assessment

QUALITY CONTROL & TRAINING WALL CHARTS

Ball Grid Array Soldering Guide - X-Ray inspection guide of satisfactory BGA
solder joints and process defects

Exerts from BGA report:

Cleaning of assemblies featuring BGA devices may seem at first consideration to
be fairly easy due to the large standoff height achieved by the balls. The
difference between fine pitch QFP and BGA devices is that it is initially
difficult to get any cleaning solution under the parts and then remove it. This
is due the leads preventing easy passage of the solution. The package standoff
height from the board for a QFP is normally between 0.005"-0.015" which is not
normally a problem. In the case of BGA the standoff height is 0.020" but the
balls then obstruct the easy passage of the cleaning solution under the device
and also impede its exit. 

A simple trial to examine this effect involved mounting different types of BGA
components on a glass plate then passing them through a batch cleaning unit.
Visual examination then showed the effectiveness of solution penetration and
removal. Trials repeating this experiment using a spray can showed that flux can
easily be flushed out from under the devices. Video taping this experiment
provided a good indication of the cleaning potential. As the parts increase in
size the effective drying of water based products may be more difficult but can
easily be assessed using this technique.
 
The use of cleanliness testing equipment to monitor ionic residues may also be
used with very few envisaged problems. If required, parts may be attached to a
piece of glass with flux placed under the device. This may then be tested to see
the effectiveness of the test method. Using a specific quantity of sodium test
solution would allow a specific reading to be obtained which could provide
evidence of the equipment's ability to detect contamination.

The test boards used in this project are being included in a further SMART Group
solder joint reliability study. This is being conducted on surface mount solder
joints mounted on alternative solderable finishes and is due to be completed in
early 1995. As the BGA test boards were not originally designed to be included
in this study the samples are being subjected to the same environmental test
conditions without any electrical monitoring. At the completion of the test the
boards are to be examined by microsectioning the joints. 


Bob Willis
Electroinc Presentation Services
2 Fourth Avenue, Chelmsford, Essex CM1 4HA. England.
Tel: (44) 01245 351502
Fax: (44) 01245 496123
Home Page: http:// Still not working, who said using computers was easy!!!!!