Browse Prior Art Database

Flux Residue On Line Monitor

IP.com Disclosure Number: IPCOM000107619D
Original Publication Date: 1992-Mar-01
Included in the Prior Art Database: 2005-Mar-22
Document File: 3 page(s) / 75K

Publishing Venue

IBM

Related People

Enno, RS: AUTHOR [+2]

Abstract

Disclosed here is a monitoring technique which allows direct, nondestructive measurement of flux/solder residue, on assembled printed circuit boards (PCB). The method, based on an alternating current (AC) electrical measurement, provides data that is directly related to both the corrosivity and the conductivity of residues which are the primary factors determining dendritic growth and possible field failures.

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Flux Residue On Line Monitor

       Disclosed here is a monitoring technique which allows
direct, nondestructive measurement of flux/solder residue, on
assembled printed circuit boards (PCB).  The method, based on an
alternating current (AC) electrical measurement, provides data that
is directly related to both the corrosivity and the conductivity of
residues which are the primary factors determining dendritic growth
and possible field failures.

      AC impedance analysis is based on the application of a small
amplitude, sinusoidal voltage (such that the applied voltage does not
perturb the system being measured) at various frequencies, with
simultaneous measurement of the resultant current.  If the voltage is
applied across two conductors, (e.g., pads on PCB), then the current
response is dependent upon the impedance between the leads (Figure
1).  If there is conductive flux residue between the pads, then the
impedance is lower than if the card is clean.  The total impedance Z
of the system may represented as the parallel combination of a
resistance R and a capacitance C where w is the frequency and j is
!-1 (e.g., 1).
     1/Z = 1/R + -jwC                              (1)

      There are two important criteria required in order to apply
impedance techniques to the measurement of flux residues.  First, the
frequency range of use is much lower than one generally associates
with impedance measurements for conductivity.  ...