3. Flux residue test

1) Stain observation method

It can be implemented according to IPC-TM-650-2.3.38.

The size of the test sample should be greater than 50mm x 75mm, using a spectral or HPLC grade acetonitrile or other solution as the test liquid. Using a pipette, slowly (0.25-0.5) mL of the test solution was dropped on the surface of the sample each time to wash the sample surface of a small area and drip onto the glass slide. The test solution was blown dry under a gas-free air or nitrogen flow, and the washing was repeated until the amount of the test solution reached 2 mL/cm 2 . Observe the glass slides and see if there is any residue left in the wash.

2) Infrared spectrophotometer test method

It can be implemented according to IPC-TM-650-2.3.39.

The test equipment is an infrared spectrophotometer (2.5μm-16μm), KRS-5 or ZnSeMIR.

The test solution is spectral or HPLC grade acetonitrile or other solvents.

Samples were prepared on MIR tablets in the same manner as Stain Observations, and the same volume of acetonitrile was dropped onto another MIR tablet as a reference. Compare the sample spectrum with the reference spectrum. If the two are different, the sample is contaminated.

3) UV spectrophotometer test method

It can be implemented according to IPC-TM-650-2.3.27.

The test instrument is a UV spectrophotometer.

The test solution was HPLC test solution plus 1.0% phosphoric acid plus 0.1% water.

The rosin in the solder paste or flux used was extracted by Soxhlet extraction and formulated into standard samples with residual contents of 0.002%, 0.004%, 0.006%, 0.008%, and 0.010%, respectively. The UV spectrophotometer was used at 241 nm wavelength for testing and working curves. Add 100 mL of test solution to a clean plastic bag and shake it for 10 minutes before testing. If the absorption coefficient is out of range, add 100 mL of test solution to the plastic bag and shake it for 10 minutes before testing. If the absorption coefficient is still out of range, repeat the test. 100 mL of the test solution was added to the plastic bag until the absorption coefficient was less than 3.000. The residual concentration was determined using the working curve. The residue content is calculated according to formula (6):

4) High performance liquid chromatography

It can be implemented according to IPC-TM-650-2.3.27.1.

The test instrument is a high performance liquid chromatograph.

The test solution was 75% isopropyl alcohol (HPLC grade) plus 25% deionized water (18.3 MΩ.cm) (volume ratio).

(75-200) mL of the test solution was injected into a plastic bag, placed in a test sample and heat-sealed, and placed in hot water of (80±5)0C for 1 hour to test the standard sample and the sample solution, respectively.

Instrument test conditions are as follows:

A, wavelength: 220nm, 240nm;

B, column temperature: 600C;

C, eluent: 60% acetonitrile plus 40% water (volume ratio);

D, flow rate: 2mL/min;

E, injection volume: 10 mL.

The data is processed according to equations (7) and (8):

C=(S1*C0*V0)/(S0*V1) (7)

Where: C-sample solution residue concentration, mg / L;

S1 - the area of ​​the sample solution peak;

Concentration of C0-standard sample, mg/L;

V0-standard sample injection volume, mL;

The integrated area of ​​the S0-standard front;

V1-sample solution injection volume, mL.

Residue content μ(g/cm2)=(C*V/S)*1000.......(8)

Where: C-sample solution residue concentration, mg / L;

V-sample solution volume, mL;

S-standard area, cm2.

4. Surface insulation resistance test method

1) Test method for surface insulation resistance of flux

According to GB/T 9491 or reference IPC-TM-650-2.6.3.3.

A, insulation resistance before welding

Separately, 0.3 mL of the flux sample was uniformly added dropwise to the three prepared test pieces, and they were taken out in an 850C oven for 30 minutes, and placed in a test chamber at 400C and relative humidity of 90% to 95% for 96 hours. At room temperature, relative humidity of 90% (with potassium tartrate saturated solution) in the conditions of recovery 1h, with a high resistance meter (ranging 106Ω-1017Ω, voltage of 500VD.C) as shown in Figure 1-2, 2- Insulation resistance between 3, 3-4 and 4-5 points (reading after 1 min), taking the average value of three specimens as the insulation resistance before welding.

B, insulation resistance after welding

Separately, 0.3 mL of the flux sample was uniformly dropped onto three prepared test pieces, floated on a 2350C solder tank for 3 seconds (online pavement downwards), and then placed in a test chamber at 400C relative humidity of 90% to 95%. Medium, hold for 96 hours, remove it, and recover it for 1 hour at room temperature and relative humidity of 90% (with saturated potassium tartrate). Use a high resistance meter (range: 106Ω-1017Ω, voltage: 500VD.C) Measure the insulation resistance between 1-2, 2-3, 3-4 and 4-5 points separately (reading after 1 min) and take the average of the three test pieces as the insulation resistance after soldering.