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Browse Prior Art Database

Test Method to Evaluate Solder Slump

IP.com Disclosure Number: IPCOM000122473D
Original Publication Date: 1991-Dec-01
Included in the Prior Art Database: 2005-Apr-04
Document File: 3 page(s) / 123K

Publishing Venue

IBM

Related People

Shahim-Aeen, S: AUTHOR

Abstract

Disclosed is a method for testing the rheology of solder paste by quantitatively measuring solder slump to determine if it is within the application specification limits. It permits the checking and verification of the consistency and properties of solder paste which affect the yield and cycle time of the solder screening process.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 51% of the total text.

Test Method to Evaluate Solder Slump

      Disclosed is a method for testing the rheology of solder
paste by quantitatively measuring solder slump to determine if it is
within the application specification limits.  It permits the checking
and verification of the consistency and properties of solder paste
which affect the yield and cycle time of the solder screening
process.

      The trend in the manufacture of solder paste is towards high
metal content, finer powder size and higher viscosity. These are
mainly to satisfy requirements for fine line printing.  Consequently,
the rheology of the paste is designed to prevent slump.  However,
there are applications where lower metal content, lower viscosity and
"controlled" slump are desirable to avoid a high level of rework.
Viscosity measurement alone is not adequate to provide sufficient
information to the process engineers for reliable and established
Statistical Quality Control Procedures. This article cites a
technique designed to complement viscosity measurements to yield a
reliable and controlled paste meeting stringent performance criteria.

      Solder pastes have become sophisticated in order to meet fine
line printing and reflow requirements.  The flux agent, particle
size, morphological characteristics, and metal loading have been
considered carefully.  Solder paste is thixotropic and the apparent
viscosity depends on the following factors:
1- temperature      2- rate of shear    3- previous shear rate
history
4- humidity (moisture content)          5- process history and steps
6- metal content and composition        7- solvent addition
8- hydrogen bond formation within polymers of the flux vehicle
9- structure and dispersion of the gel agent within flux vehicle

      Thus viscosity measurement does not necessarily provide an
accurate and reliable control parameter.  Consequently, solder
manufacturers allow up to 14 days for the viscosity to recover and
stabilize before carrying out a final viscosity measurement.  Should
the viscosity be outside the spec limits, corrective actions are
taken to bring the viscosity within the limits.  These actions always
affect the rheological characteristics of the solder paste leading to
slumping, one of the reasons why a solder paste with the correct
viscosity behaves differently from batch to batch. Rheologists fail
to agree on a method to specify and control the rheology of the
paste.  One reliable way to improve the process capability is to
establish limits on the viscosity of the paste within which slumping
is not a problem, then to ensure the paste remains within these
limits with allowance for any aging process which takes place during
the shelf life of the paste.  Viscosity measurements using a rotating
spindle are of limited value, since the spindle does not apply a
uniform shear stress across the entire cross section of the paste.
Thus viscosit...