Why do you want to use lead-free soldering for electronic trade SMT patches?

- Sep 18, 2019-

Why do you want to use lead-free soldering for electronic trade SMT patches?

Why do you use lead-free soldering in electronic product SMT processing? When we manufacture electronic equipment, whether it is domestic sales or exporting abroad, we will review the hazardous substances including lead, indicating people's awareness of environmental protection and life. The degree of attention is constantly improving. Jingbang Electronics, which focuses on high-end SMT chip processing for 12 years, leads everyone to understand the lead-free process in SMT chip processing.

Readers who are sure to be electronic products are no strangers to ROHS. When it comes to export issues, we must consider the huge market group of the EU. In the EU's review of the export of electronic products, ROHS is an indispensable item. In the ROHS certification, the requirements for electronic products are relatively strict.

The "RoHS Directive" and the "WEEE Directive" stipulate that there are 10 categories of 102 kinds of products that are included in the management of hazardous substances and management of waste recycling. The first seven products are the main export electrical products in China. Including large household appliances, small household appliances, information and communication equipment, consumer products, lighting equipment, electrical and electronic tools, toys, leisure and sports equipment, medical equipment (except for implanted or infected products), monitoring and control instruments ,vending machine.

The most important part of lead-free control is the use of lead-free soldering technology in the SMT placement process, including the use of lead-free solder paste and lead-free soldering processes.

I. RoHS restrictions on electronic products - lead-free

International standards related to it

1. IPC-1066 "Determination of Marks, Symbols and Labels for Lead-Free and Other Reportable Materials in Lead-Free Assembly, Components and Equipment" January 2005

2. IPC/JEDEC J-STD-609 "Marking, Symbols and Labels for Welded Terminal Materials for Electronic Assembly" February 2006

3. IPC/JEDEC J-STD-020D "Humidity/Reflow Solder Sensitivity Classification for Non-closed Solid Surface Mounting Components" May 2006 (Supersedes IPC/JEDEC J-STD-020C July 2004)

4. IPC-1065 Material Declaration Manual

5, (IPC-1752-1/2 "Material Declaration Form" IPC-1752-3 "Material Declaration Format User Guide"

6. IPC-1401 Material Declaration Manual (for printed circuit board manufacturing and users only)

7, JESD201 "tin and tin alloy surface coating tin whisker magnetic rate environmental acceptance requirements"

8. JESD22-A121 "Test Method for Measuring Tin Whisker Growth of Tin and Tin Alloy Surface Coatings"

9. J-STD-033 "Packaging, Transportation and Use of Moisture/Reflow Soldering Surface Mount Devices"


Second, the advantages and disadvantages of lead and lead-free

1. Lead-free solder is selected from SAC305 (Sn96.5% Ag3%Cu0.5%) and has a melting point (Liquidity m.p) of 217 °C to 221 °C. Compared with the current Sn63/Pb37 eutectic alloy (EutecticComposition), the average operating time is extended by 20 seconds, which results in a large increase in heat (Thermal Mass), which has a great influence on components and PCB.


2. The current Sn63/Pb37 reflow peak temperature is 225 ° C, wave soldering is about 250 ° C; but SAC 305 reflow temperature can only be increased to 245 ° C, wave soldering (PCB spray tin) can only be 270 ° C, to prevent parts or components Damaged at high temperatures. Even so, the effect of dissolving tin at high temperatures will destroy the metal content of the solder, causing the melting point to rise and the fluidity to deteriorate.


3. The surface tension of Sn63.Pb37 is about 380 dynes/260 ° C, the contact angle on the copper base is about 11 °, and the surface tension of AC305 is about 460 dynes / 260 ° C. The contact angle is increased to 44°; the increase in surface tension increases the cohesive force, which makes the outward adhesion smaller, which is not only easy to tombstone but also makes the tin-dispersibility and tin-up property worse; usually The Wetting Time of Sn63/Pb37 is 0.6S, while the wetting time of SAC305 is 2S.


Third, the RoHS exemption clause: lead (Pb) can continue to be used in the following cases:

1. Lead in glass materials for CRTs, electronic components and fluorescent tubes.

2, high-temperature solder containing lead (lead content exceeds 85%)

3. Lead-containing solder for server and data storage (exemption valid until 2010)

4. Lead-containing solder is used in network infrastructure equipment such as switches, signaling equipment, transmission equipment, and telecommunications network management equipment.

5. Lead in electronic ceramic devices (such as piezoelectric ceramic devices)

6. As an alloying element, the steel alloy does not exceed 0.35%, the aluminum alloy does not exceed 0.4%, and the copper alloy does not exceed 4%.


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