Surface insulation resistance measurement of circuit boards

SIR (Surface Insulation Resistance) is usually used for the reliability test of the circuit board. The method is to connect pairs of electrodes alternately to form a comb-shaped circuit (Pattern) on the printed circuit board (PCBA board), and print solder paste, and then heat it at a certain high temperature. Continue to give a certain bias voltage (BIAS VOLTAGE) in a humid environment. After a certain period of time (24H, 48H, 96H, 168H), observe whether there is an instantaneous short circuit between the lines or a slow leakage of insulation failure.

This test also helps to see if there is any residue of flux or other chemicals on the PCB surface that will affect the electrical characteristics of electronic components. Generally, we use this method to measure static surface insulation resistance (SIR) and dynamic ion migration (ION MIGRATION). In addition, it can also be used as CAF (Conductive Anodic Filament, conductive filament, anodic glass) Fiber leakage phenomenon) test.

Note: CAF mainly tests the effect of flux on the hygroscopicity of PCB board and the separation of glass fiber surface.

Surface Insulation Resistance (SIR) is widely used to evaluate the impact of contaminants on assembly reliability. Compared with other methods, the advantage of SIR is that in addition to detecting local contamination, it can also measure the impact of ionic and non-ionic contaminants on the reliability of printed circuit boards (PCBs), which is far more effective than other methods (such as cleanliness). test, silver chromate test... etc.) are effective and convenient.

Since the current circuit board wiring is getting denser and the solder joints are getting closer and closer, this experiment can also be used as solder paste Flux Availability Evaluation Reference.

Comb Pattern, comb circuit is a kind of "multi-finger" interlaced dense circuit pattern, which can be used for board surface cleanliness, green paint insulation A special circuit pattern for high-voltage testing, etc.

SIR Measurement Standard: IPC-TM-650

▼SIR experiment The test board used, a board has four pairs of electrodes connected in a comb-shaped pattern (Pattern)

▼Stagger a group of SIR experiments with pairs of electrodes When connecting into a comb-shaped pattern (Pattern) enlarged image, when measuring SIR, print solder paste on the comb-shaped pattern (Pattern), and then vertically put the SIR test board with solder paste printed on it and place it in an environmental testing machine. To add a bias voltage of 45~50VDC to its positive and negative poles, the conditions of the environmental experiment are as follows:

85+/-2℃ + 20%RH 3 hours

85+/-2℃ + 85%RH after at least 1 hour start to apply 50VDC bias< /p>

↓ Measure SIR value with 100VDC after 24 hours

< span style="font-size: 16px;">↓ Measure the SIR value with 100VDC after 24 hours (total 48 hours)

↓ Measure the SIR value again with 100VDC after 48 hours (96 hours total)

↓ Measure the SIR value with 100VDC after 96 hours (total 168 hours)