PCB Blog - PCB board cleaning effect detection method

PCB board cleaning effect detection is involved in PCB production and processing, board modification design and other board making processes. As for the method and evaluation standard of PCB cleaning effect detection, electronic processing plants and circuit board engineers should follow certain 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/T 31311. The chemical composition of cast tin-lead solder shall meet the requirements of GB/T 8012.
2) Flux flux quality should be tested from the appearance, physical stability and color of flux, non-volatile content, viscosity and density, water extraction 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 printed circuit board has not formed a unified cleaning quality standard. In developed countries more commonly used industry standards for printed circuit board cleaning quality has the following provisions.
1) J-STD-001B stipulates: A, ion contaminant content: < 1.56μgNaCl/cm2; B, flux residue: < 200μgNaCl/cm2, secondary < 100μgNaCl/cm2, tertiary < 40μ gnNA-Cl /cm2; C, average insulation resistance > 1 rated 108 ω, standard deviation of (log10) < 3.
2) IPC-SA-61 according to the value specified in the process.
3) Mil-STD-2000A stipulates ionic contaminant content < 1.56μgNaCl/cm2. In addition, in mil-P-28809 specification, it is stipulated that the resistivity of cleaning or cleaning solution can also be used as the criterion of cleaning degree. The resistivity of cleaning solution is greater than 2 rating 106 ω. Cm is clean, otherwise it is not clean. This method is suitable for cleaning process monitoring. Due to the emergence of various commercial surface ion contamination testers, the test results of different testing systems are different, but they are all higher than manual test results. Therefore,, the concept of equivalent coefficient is proposed to achieve the comparability of test results of different systems.
4) content of the process ion contaminant content, flux residual process A < 1.5μgNaCl/cm2 < 217μg/ plate process C < 2.8μgNaCl/cm2 < 2852μg/ plate process D < 9.4μgNaCl/cm2 < 1481μg/ plate average insulation resistance value > 1 rating 108 ω, Standard deviation of (log10) < 3 > 1 rating 108 ω, 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 without the use of a magnifying glass, direct observation of the printed circuit board surface with the eyes should be no obvious residues.
3.2 Surface ion contamination test method.
1) Extraction solution resistivity (ROSE) Test method The principle of extraction solution resistivity test method is to take 75% isopropyl alcohol and 25% deionized water (volume ratio) as the test solution, wash the printed circuit board surface and make the pollutants remaining on the printed board surface dissolve into the test solution. Because the positive and negative ions in these pollutants reduce the resistivity of the test solution, the more ions dissolved in the test solution, the more the resistivity decreases, and the two have an inverse function relationship.

(1) It is the use of this functional relationship, by measuring the resistance value of test solution before and after washing and the volume of test solution used, can calculate the content of residual ions on the surface of printed circuit board, and the stipulation is expressed by NaCl equivalent per square centimeter, namely μgNaCl/cm2. Manual test method can be performed according to GB/T 4677.22, or refer to IPC-TM-650 2.3.25, MIL-STD-2000A. Measure the test solution at a ratio of 1.5ml per square centimeter of printed circuit board. The resistivity of the test solution must be greater than 6M ω.cm and the surface of the printed circuit board should be washed in a small flow until all the test solution has been collected into the beaker. This process should take at least 1 minute. The resistivity of the test solution was measured with a conductance bridge or an instrument with the same range and precision, 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, μgNaCl/cm2; 2- The resistivity of the sample containing 1.56μgNaCl/cm2, M ω.cm; Resistivity of p-collecting liquid, M ω.cm; When the resistivity value of 1.56 is 2M ω.cm, the corresponding NaCl equivalent, μg/cm2, is contained in the unit area of the sample. Instrument test method can be performed according to IPC-TM-650-2.3.26 or refer to IPC-TM-650-2.3.26.1. By measuring the temperature and density of the test solution to determine the isopropyl alcohol content, and make it up to 75%. Start the purification pump and purify the liquid using an ion exchange column until the resistivity of the test liquid reaches or exceeds 20M ω.cm. After the system is verified correctly, inject an appropriate amount of test liquid into the test tank, put in the test sample, and start the test pump to measure the resistivity of the test liquid until the resistivity reaches stability. According to the different structure of test loop, the test can be divided into static test method and dynamic test method. The loop of static test method consists of test groove, resistivity test probe and test pump.

(3) is calculated. Where: Wr- NaCl equivalent per square centimeter, μgNaCl/cm2. V- Volume of test fluid in the test loop, L; P1 -- Final resistivity value of test fluid, ω.cm. S- Area of test sample (l to W to 2), cm2. Po - Initial resistivity value of the test fluid, ω.cm. C-- Isopropyl alcohol content in test solution (75%); A, B-- experimental constants. The test loop of dynamic test method consists of test groove, resistivity test probe, test pump and ion exchange column. Because the test solution is continuously purified by the ion-exchange column throughout the test process, the resistivity of the test solution should be continuously measured and accumulated during the test.

(4). Where: N-- the amount of ions in the test solution, moL; K - experimental constant; V- Volume of test fluid in the test loop, L; Test resistivity value at 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 pollutants < 25mg/kg; D, polyethylene plastic bag: Cl- < 3mg/kg; E, deionized water: 18.3M ω.cm, Cl- < 50mg/kg; F, isopropanol: electron 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 thermal sealing, the printed circuit board should be soaked in the extraction solution, the printed circuit board was placed in a hot water bath of (80±5) 0C for 1 hour.

(5). Where: Wr-- the content of some ion per square centimeter area, μgNaCl/cm2. C- The content of a certain ion in the extraction solution tested according to the standard sample, mg/kg; V0- Volume of extraction liquid injected into polyethylene plastic bag, mL; V1- Volume of extraction solution injected into ion chromatograph for testing, mL; S-printed circuit board area (l/W / 2), cm2 on PCB board.