PCB (printed circuit board) is playing a fundamental role in today’s life. It’s the base and the highway of electronic components. As far as this is concerned, the quality of PCB is very critical without doubt.
To inspect the quality of PCB, several reliability tests must be done. The following paragraph is an introduction of the tests.
The IPC (Institute of Printed Circuits) carried out a test methods standard which lists a series of detailed criteria of PCB quality tests. According to the criteria, there’re mainly 9 tests we should do.
1. Ion contamination test
Aim: examine the number of ions on the surface of board to decide if the cleanliness of board is qualified.
Method: clean the surface of sample using propanol of 75% concentration. The ion can dissolve into propanol and thus change its conductivity. Record the change of conductivity to determine the concentration of ions.
Criterion: less than or equal to 6.45 ug.NaCl/sq.in
2. Chemical resistance test of solder mask
Aim: examine the chemical resistance of solder mask
Method:
- Drop q.s. (quantum satis) dichloromethane on the surface of sample.
- After a while, wipe the dichloromethane using a white cotton.
- Check if the cotton get dyed and if the solder mask dissolved.
Criterion: no dye or dissolution.
3. Hardness test of solder mask
Aim: examine the hardness of solder mask
Method:
- Put the board on a flat surface.
- Use the standard test pencil for a range of hardness to scratch on board until there’s no more scratch.
- Record the minimum hardness of pencil.
Criterion: the minimum hardness should be above 6H.
4. Wire strip-off intensity test
Aim: examine the force that can strip off copper wire on the board
Equipment: strip-off intensity tester
Method:
- Strip off the copper wire from one side of substrate for at least 10mm.
- Place the sample board on tester.
- Strip off the rest of the copper wire using a vertical force.
- Record the force.
Criterion: the force should exceed 1.1N/mm.
5. Solderability test
Aim: inspect the solderability of solder pads and through holes on the board.
Equipment: solder machine, oven and timer.
Method:
- Bake the board in oven for 1 hour at 105℃.
- Dip flux.
- Flatly put the board into the solder machine at 235℃, and take it out after 3 seconds, check the area of solder pads that dip tin.
- Vertically put the board into the solder machine at 235℃, and take it out after 3 seconds, check if the through holes dip tin.
Criterion: percentage of the area should be more than 95. All the through holes should dip tin.
6. Withstanding voltage test
Aim: test the voltage-withstand ability of board.
Equipment: withstanding voltage tester
Method:
- Clean and dry the sample.
- Connect the board to the tester.
- Increase voltage to 500V DC (direct current) at a speed no more than 100V/s.
- Keep it at 500V DC for 30s.
Criterion: there should be no breakdown on the circuit.
7. Tg (glass transition temperature) test
Aim: examine the glass transition temperature of board.
Equipment: DSC (Differential scanning calorimetry) tester, oven, dryer, electronic scale.
Method:
- Prepare the sample, the weight of it should be 15-25mg.
- Bake the sample for 2 hours at 105℃ in oven, then put it in dryer to cool to room temperature.
- Put the sample onto the sample stage in DSC tester, set the temperature increase rate at 20℃/min.
- Scan for 2 times, record the Tg.
Criterion: the Tg should be above 150℃.
8. CTE (coefficient of thermal expansion) test
Aim: evaluate the CTE of board.
Equipment: TMA (thermal mechanical analysis) tester, oven, dryer.
Method:
- Prepare the sample on a size of 6.35*6.35mm.
- Bake the sample for 2 hours at 105℃ in oven, then put it in dryer to cool to room temperature.
- Put the sample onto the sample stage in TMA tester, set the temperature increase rate at 10℃/min and the final temperature at 250℃
- Record the CTE.
9. Heat resistance test
Aim: evaluate the heat resistance ability of board.
Equipment: TMA (thermal mechanical analysis) tester, oven, dryer.
Method:
- Prepare the sample on a size of 6.35*6.35mm.
- Bake the sample for 2 hours at 105℃ in oven, then put it in dryer to cool to room temperature.
- Put the sample onto the sample stage in TMA tester, set the temperature increase rate at 10℃/min.
- Raise the temperature of sample to 260℃.
- Keep the temperature and record the time until measling or delamination occurs.
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