Glossary of Residue Testing Terms

If you’re new to the world of residue testing, a number of the terms you’ll hear may not make sense to you. Here’s a glossary to help you make sense of it.


BIC Tester
BIC (or Bulk Ion Contamination) testers indicate how conductive a solution is, but not which elements are present in the solution.


Conductive Residue
Residues that are conductive tend to cause electrical leakage, ultimately causing an assembly to fail. These conductive residues are often the result of flux activators.


Destructive Tests
A destructive test is a test method that destroys the board being tested, e.g. cross-sectioning.


Flux Residue
A common and damaging residue source that afflicts printed circuit board assemblies. Common flux residues are chloride and weak organic acids (including adipic and succinic acids). They are a direct result of flux activators, and only cause issues if not allowed to fully complex and volatize. For more information, see What is a Flux Residue?


Ion Chromatography
An analytical test method that takes a solution and separates, identifies, and quantifies each individual contaminant species. By species, we refer to basic elements, such as chloride or bromide, or molecular compounds, such as sulfates or weak organic acids. We consider it the best cleanliness test method. For more information, see Ion Chromatography for Electronic Assemblies and Bare Boards.


Ionic Contamination
Ionic contamination is considered present if any electrically-conductive residue is remaining on an assembly.


No-Clean Flux
A flux technology that leaves behind residues that are not conductive, and therefore not usually harmful. However, in some instances, it may still be helpful to clean a no-clean assembly.


SIR Testing
SIR stands for surface insulation resistance. It’s a method of testing that involves taking a substrate designed for SIR testing, soldering wires to the test pattern, and putting it in a temperature-humidity chamber. Then, an electrical potential is applied and the insulation resistance is periodically measured.


Water Soluble Flux
A water soluble flux is a flux technology that is designed to be cleaned after soldering. If not properly cleaned, the residues from water soluble fluxes can cause reliability issues.


White Residue
A sometimes-harmful-sometimes-not residue left behind after soldering. White residues do not always qualify as a defect. Whether they do or do not is dependent on their location on the board and their conductivity.