Ion Cleanliness Test of Printed Circuit Board (PCB)

Importance of ion cleanliness

In the electronic manufacturing industry, the ionic cleanliness of printed circuit board (PCB) is a key index to evaluate its quality and reliability. In the production process, PCB goes through many processes such as electroplating, wave soldering, reflow soldering and chemical cleaning, which may introduce ionic pollutants, thus affecting the function and long-term reliability of electronic products.

The most common hazards of ion pollution include surface corrosion and crystal growth, which may eventually lead to short circuit, lead to excessive current passing through the connector, and cause damage to electronic products.

Therefore, it is of great significance to accurately detect ion cleanliness and determine the source of pollutants for reducing the defective rate of products and enhancing the competitiveness of enterprises.

Common sources of pollutants include flux residues, ionized surfactants, ethanol, aminoethanol and human sweat. These pollutants have various forms and pose potential risks to electronic products. It has become a key link in electronic manufacturing industry to locate pollution sources through scientific testing methods.

Overview of ion cleanliness testing methods

1. Anion test method (IPC-TM-650, 2, 3, 28)
The anion-cation test method is one of the widely used ion cleanliness testing methods at present. Its core principle is to soak the sample surface with a mixed solution of isopropanol and water in a certain proportion, so that the pollutants on the sample surface can be dissolved in the solution.

Then, the types and contents of anions and anions and organic acids in the solution were detected by professional analytical instruments, so as to evaluate the pollution degree of the sample. Test results are usually expressed in micrograms per square centimeter (ug/cm). This method can accurately identify the species and content of each ion, which is helpful to locate the pollution source. For example, when analyzing short circuit fault, the pollution source can be judged by the abnormality of specific ion content.

2. Sodium chloride equivalent method (IPC-TM-650, 2, 3, 25C)
Sodium chloride equivalence rule is another commonly used method to test ion cleanliness. The core of this method is to remove the residues left in the process from electronic components by using ultra-pure extraction solution. In this method, the extraction liquid consisting of 75% isopropanol and 25% deionized water is used to extract residues from the surface of electronic components. The level of pollutants was evaluated by measuring the conductivity or resistivity of the extract, and the result was expressed as the equivalent concentration of sodium chloride (µgEq NaCl/cm²). The limitation of this method is that it can't identify the specific ion species and their contents, and can only reflect the overall pollution level.

Selection strategy of test method

In practical application, it is very important to choose the appropriate ion cleanliness testing method.

If it is necessary to make clear the types and contents of pollutants, so as to locate the pollution sources and formulate improvement measures, it is suggested to adopt the anion-cation test method. For example, the high content of fluorine (F), chlorine (Cl) and bromine (Br) may be due to the solder resist in the welding process; If the organic acid content is high, it may be introduced by ethanol or aminoethanol used in the cleaning process.
If only the overall pollution level needs to be evaluated, the sodium chloride equivalent method can be used. This method is simple to operate, but it can't provide specific ion information.
Enterprises should combine their own needs and weigh the advantages and disadvantages of the two methods to choose the most suitable test scheme.

In order to ensure the accuracy and reliability of ion cleanliness test results, sample preparation and treatment should meet the following conditions:

1. The surface area of the sample is more than 100 square centimeters, so as to ensure that there is enough sample surface in contact with the extraction liquid during the test, so as to obtain representative test results.

2. Before testing, the sample should be protected from external pollution, and its surface state should be consistent with the actual production environment, so as to truly reflect the ion cleanliness level of the product. Jinjian Laboratory strictly abides by the specifications and standards to ensure the accuracy and reliability of the test results.

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Ion cleanliness detection plays an important role in quality control of electronic manufacturing. Through scientific testing methods, enterprises can effectively identify and control ion pollution and improve product reliability and quality. As the mainstream methods, the anion-cation test method and the sodium chloride equivalent method have their own characteristics, so they should be selected reasonably according to the actual needs. At the same time, strict compliance with sample handling and testing standards is the key to ensure the validity of the results.

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