Internal and external cleanliness of products

Product cleanliness testing- qualitative and quantitative methods

Product cleanliness testing is a very important element in the quality assessment of many components, especially those having contact with operating fluid. Such tests are carried out in a clean room of ISO 6 cleanliness class (according to ISO 14644).
The basic factors determining the purity of the tested object are: mass of insoluble impurities, mass of soluble impurities, amount of insoluble impurities of a certain size and type of contamination. In the case of insoluble (solid) impurities, it is possible to divide them according to their nature: metallic, non-metallic and fibers, as well as by chemical composition. In order to determine these properties, an appropriate extraction liquid is selected (it must be compatible with the component material) and method of pollutants extraction is selected: agitation, pressure washing, ultrasonic techniques, washing on functional test benches reflecting the working parameters of the test object. The choice of the extraction method depends on the characteristics of the tested object and on the specified properties: internal/external/overall purity.
 
Extracted pollutants are analyzed by the following methods:
 
  • gravimetric – the mass of contaminants
  • microscopic – the quantity and size of the contaminants
  • scanning electron microscopy (SEM)– the chemical composition of the impurities
  • infrared spectroscopy – the chemical composition of organic impurities

Devices

 

BOSMAL is the only laboratory in Poland accredited for testing of cleanliness according to ISO 16232, VDA 19.1 and DIN 8964-1

 

Testing norms

  • ISO 16232
  • DIN 8964-1
 

Testing norms from the industry and customers’ own norms

  • VDA 19.1, QV 11111, DBL 6515, DBL 6516, PV 3347, PV 3370, PV 3336, VW 01134, VW 01137, Volvo STD 107-0002, Scania STD 4189, GMW 16037, NW 22-10-202, SAE J1726, Continental TST N 002 02.22, Wabco JED 593, BWS 42001, Renault 34-07-012, Renault 34-07-025 and others.

Evaluation of cleanliness by surface tension test

One of the simple and fast methods of determining the cleanliness of surfaces is to test the surface tension by applying test inks / markers.
 
Surface contamination, especially that resulting from metal alloys which are formed in the course of production process, reduces adhesion of paints, adhesives or galvanized coatings.
 
Clean surfaces have a material- specific surface tension. Clean surfaces have high surface energy, while in case of contaminated items surface energy proves to be much lower. 
It is assumed that a correct value of surface tension for metallic surfaces should be min. 44 mN / m for processes such as gluing, welding or coating to be effective. Typically, for cleaned surfaces, depending on the cleaning process applied, the surface tension ranges from 38 mN / m to more than 70 mN / m. In case of oily surfaces, the surface tension ranges from 25 to 35 mN / m.
 
The cleanness assessment technique related to surface tension consists in applying a test ink with an appropriate value of the surface tension to the tested surface. Observing the behaviour of the stroke of ink on the surface allows to determine the minimum value of the surface tension of the tested item.
 
 

Measurement of extractable ionic contamination

Laboratory also performs cleanliness tests based on checking the presence of ionic contaminants on the analyzed surfaces. Various types of samples can be tested, including printed circuit boards, enabling the determination of contaminants (e.g. soldering residues, residues from galvanic processes) that may lead to surface corrosion, affect the functionality of components or significantly impede further production processes .
 

Examples of research may include:

  • preliminary assessment of the overall cleanliness assessment of printed circuit boards surfaces, assemblies of printed circuit boards or their components, based on measurement of the electrolytic conductivity of the solvent extract obtained from washing the tested surface. The test is carried out in accordance with IPC-TM-650 No. 2.3.25 - manual extraction method. The result of the test is the degree of surface contamination expressed as equivalent of dissolved salt in µg NaCl / surface area tested.
  • detailed evaluation of the ionic purity of tested surface. In the test a set of two ion chromatographs and appropriate standard solutions are used. On this basis qualitative and quantitative analysis is possible, and determination of main anions (including chlorides and bromides) as well as main cations (sodium, ammonium, potassium). Implemented methodology enables determination of ions at low concentration levels (in the order of 1 mg / L). Additionally, determination of anions: fluoride, chloride, nitrite, nitrate, bromide, phosphate and sulphate is possible. Among the cations, it is also possible to determine: lithium, calcium and magnesium. The test is carried out for aqueous solutions, solutions from surface washing or solvent extraction performed at room or elevated temperature, e.g. in closed containers or bags with appropriate cleanliness level (e.g. according to the IPC-TM-650 method No. 2.3.28.2).

Equipment:

Ion chromatograph Metrohm - 930 Compact IC Flex
Conductometer Elmetron CC-505
Temperature chamber
Water bath
 

Testing norms and methods:

IPC-TM-650 No. 2.3.28.2
IPC-TM-650 No. 2.3.25 (manual extraction method)
PN-EN ISO 10304-1:2009
PN-EN ISO 14911:2002
Document No. Title/Description
ISO 16232 Road vehicles - Cleanliness of components and systems
VDA 19.1 VDA Volume 19 Part 1, Inspection of Technical Cleanliness - Particulate Contamination of Functionally Relevant Automotive Components
DIN 8964-1 Circuit components for refrigerating systems - Part 1: Testing
IPC-TM-650, Test Method 2.3.28 Test Method 2.3.28 Ionic Analysis of Circuit Boards by Ion Chromatography
IPC-TM-650, Test Method 2.3.25 Detection and Measurement of Ionizable Surface Contaminants by Resistivity of Solvent Extract (ROSE)
ISO 10304-1 Water quality — Determination of dissolved anions by liquid chromatography of ions — Part 1: Determination of bromide, chloride, fluoride, nitrate, nitrite, phosphate and sulfate
ISO 14911 Water quality — Determination of dissolved Li+, Na+, NH4+, K+, Mn2+, Ca2+, Mg2+, Sr2+ and Ba2+ using ion chromatography — Method for water and waste water