Step by step process of lead-free PCBA processing

Step by step process of lead-free PCBA processing

Lead free PCBA processing refers to PCBA that does not use lead at any stage of manufacturing. Traditionally, lead is used in PCB welding. However, lead is toxic and therefore harmful to humans. In view of its consequences, the European Restriction of Hazardous Substances Directive (RoHS) prohibits the use of lead in PCBA processing. There is almost no difference in PCBA processing when lead is replaced by less toxic substances. This article introduces the process of lead-free PCBA step by step.

Lead free PCBA guidelines
The lead-free PCBA processing process is divided into two basic parts, namely, the pre assembly process and the active assembly process. The steps involved in the lead-free PCBA processing are as follows.

Pre assembly steps
Lead free PCB manufacturing involves three basic pre assembly steps. These steps lay the foundation for error free and accurate PCB assembly. The pre assembly steps for lead-free PCB assembly are as follows.

Analysis is a process similar to prototype. The manufacturer takes the finished lead-free PCB as the prototype. This can be a normal operating PCB, or an invalid PCB or dummy part. The template used for assembly is tracked by the contour. Lead free component designs are compared to prototypes to ensure compatibility with components.

Solder paste inspection:
Because lead-free solder joints have a metallic appearance, which is very different from lead based solder, it is important to carefully inspect them. Check PCB shape and solder paste according to IPC-610D standard to ensure that lead-free solder joints are firm and firm. The moisture content was also tested in this step because the boards were exposed to high moisture content in lead-free soldering compared to traditional soldering.

Bill of Materials (BOM) and component analysis:
In this process, the customer must verify the Bill of Materials (BOM) to ensure that the components are made of lead-free materials. Lead free components are susceptible to moisture and should therefore be baked in an oven by the manufacturer. Once the necessary steps have been performed, the actual lead-free assembly begins.

Active assembly steps
In the process of active assembly, PCB assembly is actually carried out. The steps involved in active lead-free assembly are as follows.

Template placement and solder paste application:
In this step, the lead-free template in the forming stage is placed on the board. Then apply lead-free solder paste. Generally, the lead-free solder paste material is SAC305.

Component installation:
After applying the solder paste, install the assembly on the plate. Component placement can be done manually or automatically. This is a pick and place operation, but the components used need to be confirmed and marked in the BOM validation phase. The machine or operator selects the labeled components and places them in the designated location.

Perform lead-free through-hole or manual welding at this stage. No matter which process, THT or SMT, welding must be lead-free.

Placement of circuit boards in the reflux furnace:
RoHS compatible PCBs require high temperature heating to melt solder paste evenly. Therefore, PCBs are placed in a reflow furnace where the solder paste melts. In addition, the plates are cooled at room temperature to cure the melted solder paste. This helps to hold the components in place.

Testing and packaging:
PCB has been tested according to IPC-600D standard. Test the solder joints in this step. The visual inspection is followed by AOI and X-ray inspection. Perform physical and functional testing before packaging.

For lead-free PCB packaging, it is very important to use anti-static discharge bags. This is very important to ensure that the final product will not be subject to static charge during transportation.

However, despite a thorough understanding of lead-free PCBA processing, it is still up to experts to improve it. Hengtian Weiye is a lead-free PCB manufacturing company, which uses RoHS compliant FR4 materials for PCB manufacturing. Follow IPC-A-600D and ANSI/J-STD-001 lead-free PCB manufacturing standards.

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