1. Purpose: Standardize the procedure for setting the furnace temperature curve to ensure the quality of SMT products.

2. Scope: Applicable for setting the temperature curve of lead solder paste used by SMT manufacturers.

3. Responsibilities:

Engineering Department: Configure the furnace temperature following this procedure.

Quality Department: Verify the furnace temperature settings according to this procedure.

4. Assignment content:

4.1 Test method: Identify the heat capacity category based on the product being produced. Use either the customer’s finished product or a matching blank temperature measuring board to test if it meets the curve requirements for that category; if so, the actual production will also meet the reflow curve requirements.

4.2 Setting principles:

4.2.1 SMT produces new products and cannot provide scrap veneers for furnace temperature testing for all products. Use the following methods to set furnace temperature parameters.

4.2.2 The solder paste temperature curve requirements are as follows:

4.2.3 Component requirements: The set temperature must align with the reflow profile of all SMD devices. Excessive temperature can potentially damage components; for relays, crystal oscillators, and thermal devices, ensure the temperature meets the lower limit of soldering requirements.

4.2.4 Layout and packaging of components: Focus on the device packaging form. For boards with high component density or those with PLCC, BGA, and other components with significant heat absorption and poor thermal uniformity, consider preheating time and the upper temperature limit, and divide the PCB into levels.

4.2.5 PCB thickness and material: Thicker PCBs require longer soaking times; for special materials, heating conditions must be met, focusing on the maximum temperature and duration they can withstand during reflow.

4.2.6 Considerations for double-sided reflow: For double-sided reflow soldered boards, first produce the side with a smaller overlap area between the component pad and the PCB pad. If the component numbers are similar, prioritize production of the side with fewer components. When setting the temperature for the second surface, ensure a 5-10 degree difference between the upper and lower temperature settings if components on the first surface are prone to falling.

4.2.7 Production capacity requirements: When the chain speed setting of the reflow furnace becomes a production bottleneck, either increase the chain speed or raise the temperature of the heating zone (keeping wind speed constant) to meet production demands.

4.2.8 Equipment factors: Heating method, length of heating zone, exhaust gas emission, and intake air flow rate affect reflow efficiency.

4.2.9 Lower limit principle: To minimize temperature-related damage to components and PCB, set the lower limit of temperature while meeting welding requirements.

4.2 IPQC compares the actual measurement curve with the reflow oven curve requirements to ensure compliance.

5. Matters needing attention:

5.1 Temperature settings for each zone are reference points. Specific settings should be based on reflow oven condition and solder paste model, but the tested temperature curve must meet the specified requirements.

5.2 SMT patch processing: For continuous production of the same product, measure the furnace temperature curve once per shift. Test the curve before new product trial runs and transfers, and avoid casual changes in temperature settings (unless specified by customer requirements).

Leave a Comment

Contact

WellCircuits
More than PCB

Upload your GerberFile(7z,rar,zip)