New materials-Tin Whisker Test Solution

    In the process of lead-free component manufacturing, in order to maintain the solderability of components, pure tin plating is often used to replace the original tin lead. After a period of time, pure tin plating will grow dendritic protruding at room temperature, which called tin whisker (whisker). The tin whisker is completely different from the ion migration. It must be noted that if the length of the tin whisker is too long, it will cause short circuit between conductors or components. At present, relevant tin whisker detection standards have been formulated and environmental test methods of tin whisker can help relevant enterprises test the inhibition method of tin whisker. The method to avoid tin whiskers to meet the relevant lead-free process of heavy metal requirements and standards is urgent in the high-density construction of electronic products (mobile phones, PDA, MP3, automotive electronics, etc.). Lab Companion LTD. hopes to help customers import tin whiskers test as soon as possible, enhance and strengthen the competitiveness of the enterprise itself through the collection and sorting of relevant information.

(1) There are 13 factors affecting the growth of tin whiskers

1. Grain size

2. Residual stress

3. External stress

4. Organic matter including: carbon, sulfur, oxygen... Etc.

5. Hydrogen and water gather

6. Thermal stress

7. Electric and magnetic fields

8. Nucleation

9. Electroplating solution

10. Electroplating conditions: current density, electroplating pulse

11. Temperature

12. Humidity

13. Time

① Tin whiskers easy to grow reasons:

1. Bright tin is easy to grow tin whiskers

2-1. The surface of pure tin is vulnerable to natural crystal growth

2-2. The higher the purity of tin, the greater the chance of forming tin whiskers

3. Chemical stress is the most important driving force for the spontaneous growth of tin whiskers

② Tin whisker definition:

A. Length >10um

B. Consistent cross-section shape

C. There are tombs and horns

D. Length/width ratio >2

E. It is striped

③ Length calculation method of tin whisker:

A. JEDEC-22A121 measurement method

B. JEDEC-201&IEC method of measurement

④ Tin whisker length limitation:

<25um, <30um, <45um, <50um, <60umJESD201 For the length of the tin whisker requirements, according to different test methods, its length is also different.

(2) The inhibition or reduction of tin whiskers can be sorted out in 9 ways

1. Add a barrier layer, such as a nickel layer, between copper and tin

2. Copper → nickel → Palladium → Gold (forming a barrier layer)

3. Use a nickel-palladium lead frame

4. Mist coated tin (5um)

5. Tin plating (10um)

6-1. Spray tin or tin plating (8~12um) within 24 hours, quenching (annealing) fire (150℃) 1~2 hours (drying treatment

Post baking)

6-2. Tin plating (>7.5um) + post-drying treatment

7. Increase the silver content in tin plating

8. The temperature stress introduced in the welding process should be as low as possible

9. Reduce the copper content of pure tin or exposure to copper

(3) Introduction of tin whisker test method:

① Storage at room temperature:

1. Office room temperature, 1000h

2. 20~25℃/30~80%R.H, 1500h, 4230h

② High temperature storage:

1. 55℃/2years, 3400h

2. 90℃/400h

③ Temperature and humidity storage:

1. 50℃/85%R.H, 1500h

2. 51℃/85%R.H, 3000h

3. 55℃/80~95%R.H, 4230h

4. 55℃/85%R.H., 2000h, 4000h (1000h check once)

5. 60℃/85%R.H, 4000h

6. 60℃/87%R.H, 3000h

7. 60℃/90±5%R.H, 3000h

8. 60±5℃/93 (+2/-3) %R.H, 1000h, 4000h

9. 60℃/95%R.H, 1000h, 1500h

10. 85℃/85%R.H, 500h±4h

④ Temperature Shock (TST) :

1. -55 (+0/-10) ℃←→85 (+10/-0) ℃, 20min/1cycle, 1500cycles (Check once for 500cycles)

2. 85±5℃←→40 (+5/-15) ℃, 20min/1cycle, 500cycles

3. -35±5℃←→125±5℃, dwell for 7min, 500±4cycles

4. -55 (+0/-10) ℃←→80 (+10/-0) ℃, stay for 7min, 20min/1cycle, 1000cycles

⑤ Temperature cycle (RAMP) :

1. -40℃ (30min) ←→85℃ (30min), RAMP: 5℃/min), 2000cycles

2. -40℃ (15min) ←→125℃ (15min), RAMP: 11℃/min), 500cycles

3. -40℃ (15min) ←→125℃ (15min), RAMP: 15℃/min), 54290cycles

(4) Test equipment:

A. Constant temperature and humidity test chamber

B. Temperature shock test chamber

C. Temperature cycle test chamber