PCB board cleaning effect testing method
PCB cleaning effect testing involves PCB production and processing, PCB transformation design and other PCB manufacturing technologies ElectronIC processing plants and circuit board engineers should follow certain standards regarding PCB cleaning effect testing methods and evaluation standards The following is the correct detection method and scientific evaluation standard of PCB cleaning effect detection:
1 Raw material quality requirements
1) The chEMIcal composition of tin lead solder for pressure processing shall meet the requirements of GB/Tel: 31311. The chemical composition of tin lead solder shall meet the requirements of GB/Tel: 8012
2) Flux quality should be tested from the appearance, including physical stability and color, non-volatile components, viscosity and density, water absorption resistance, halogen content, solid content, weldability, dryness, copper mirror corrosion, insulation resistance, ion pollution and other aspects
2. printed circuit board cleaning quality requirements
At present, China's electronic industry, as the final product of PCB, has not yet formed a unified cleaning quality standard There are the following provisions in the industry standards for PCB cleaning quality commonly used in developed countries
1) J-STD-001B stimulations: A, ion contaminant content:<1.56mgNaCl/cm2; B. Flux residue:<200mgNaCl/cm2, secondary<100mgNaCl/cm2, tertiary<40m gnNA Cl/cm2; C, average insulation resistance > 1 rated 108 ? , standard deviation of (log10) < 3.
2) IPC-SA-61 according to the value specified in the process.
3) Mil-STD-2000A detergent ionic contaminant content<1.56mgNaCl/cm2. In addition, the mil-P-28809 specification specifies that the resistivity of detergent or detergent can also be used as the standard of cleaning degree The resistivity of the cleaning solution is greater than Grade 2 106 Ω Cm is clean, otherwise it will not be clean This method is suitable for monitoring the cleaning process Due to the appearance of various commercial surface ion contamination testers, the test results of different test systems are different, but they are higher than the manual test results Therefore, the concept of equivalent coefficient is proposed to achieve comparability of test results of different systems
4) Content of the process ion contaminant content, flux residual process A<1.5mgNaCl/cm2<217mg/plate process C<2.8mgNaCl/cm2<2852mg/plate process D<9.4mgNaCl/cm2<1481mg/plate average insulation resistance value>1 rating 108 ?, Standard development of (log10)<3>1 rating 108 ?,  standard deviation of (log10) < 3 Note: 1 Process A: printed board bare board -- test;  Process C: Printed board bare board - SMT - reflow welding - cleaning - test;  Process D: PCB bare board -- SMT -- Reflow soldering -- Cleaning -- Wave soldering -- Cleaning -- Testing.

3. Detection method
3.1 Visual inspection shall be carried out without magnifying glass, and there shall be no obvious residue on the surface of printed circuit board when directly observed with eyes
3.2 Surface ion pollution test method
1) Extraction solution resiliency (ROSE) Test method The principle of extraction solution resiliency test method is to take 75% isopropyl alcohol and 25% deionized water (volume ratio) as the test solution to clean the surface of the printed circuit board so that the remaining pollutants on the surface of the printed circuit board can be dissolved in the test solution Because the positive and negative ions in these pollutants will reduce the resistivity of the test solution, the more ions dissolved in the test solution, the greater the reduction in resistivity, and both have an inverse function relationship
(1) It is the use of this functional relationship. By measuring the resistance value of the test solution before and after washing and the volume of the test solution used, the content of residual ions on the surface of the printed circuit board can be calculated. It is specified to be expressed in NaCl equivalent per square centimeter, that is, mgNaCl/square centimeter Manual test method can be conducted according to GB/Tel: 4677.22, or refer to IPC-TM-650 2.3.25, MIL-STD-2000A Measure the test solution in the proportion of 1. 5ml per square centimeter of printed circuit board The resistivity of the test solution must be greater than 6 M ? cm and the surface of the printed circuit board should be cleaned with SMAll flow until all test solutions are collected into the beaker This process takes at least 1 minute Use a conductive bridge or an instrument with the same range and accuracy to measure the resistivity of the test solution, and NaCl equivalent per unit area was calculated according to formula (5-2) Wr=1.56 Review 2/p Where: Wr -- NaCl equivalent per square centimeter, mgNaCl/square centimeter; 2 - The resistivity of the sample containing 1 is. 56mgNaCl/cm2, M Ω. cm, and M Ω. cm. When the resistivity value is 1,. 56 is 2M Ω. cm, and the corresponding NaCl equivalent, mg/cm2, is included in the tissue area of the sample Instrument test method can be conducted according to IPC-TM-650-2.3.26 or refer to IPC-TM-650-2.3.26.1. The isopropanol content can be determined by measuring the temperature and density of the test solution to reach 75% Start the purification pump, use the ion exchange column to purify the liquid, until the resistivity of the test liquid reaches or exceeds 20M ? cm. After the system is correctly verified, inject an appropriate amount of test liquid into the test chamber, put in the test sample, start the test pump, and measure the resistivity of the test liquid until the resistivity reaches stability According to the different structures of the test circuit, the test can be divided into static test method and dynamic test method The circuit of static test method consists of test tank, resistivity test probe and test pump
(3) is calculated.  Where: Wr - NaCl equivalent per square centimeter, mgNaCl/cm2. V - volume of test fluid in the test circuit, L P1 - final resistivity value of test fluid, ? cm. S - Area of test sample (l to W to 2), cm2. Po - initial resistivity value of test fluid, ? cm. C - Isopropyl aluminum content in test solution (75%); A. B -- Experimental constant The test loop of the dynamic test method consists of a test cell, a resistivity test probe, a test pump and an ion exchange column Because the test solution is continuously purified by the ion exchange column throughout the test, the resistivity of the test solution shall be continuously measured and accumulated during the test
(4).  Where: N -- the amount of ions in the test solution, mole; K -- experimental constant; V - Volume of test fluid in the test circuit, test resistivity value at L P1 - t 2) Ion chromatography test method can be performed according to ipC-TM-650 2.3.28. The experimental equipment used includes: A, ion chromatograph; B. Hot water bath bag: 800C ± 50C; C. Polyethylene sealable plastic bags: extractable polymers<25mg/kg D, polyethylene plastic bag: Cl -<3mg/kg E, deionized water: 18.3M ?. cm, Cl -<50mg/kg F, isopropanol: electronic grade The printed circuit board and (100-250) mL of the extract were placed in a polythene plastic bag with 75% isopropyl alcohol and 25% deionized water (volume ratio).  After heat sealing, the printed circuit board was placed in a hot water bath of (80 ± 5) 0C for 1 hour
(5).  Where: Wr -- content of certain ions in each square centimeter area, mgNaCl/cm2. C -- content of certain ions in the extraction solution tested according to the standard sample, mg/kg V0 -- volume of the extraction solution injected into the polyethylene plastic bag, ml; V1 - Volume of the extracted solution injected into the ion chromatograph for testing, mL; S-printed circuit board area (l/W/2), cm2 Open PCB