PCB Technical - About SMT patch-furnace temperature curve operation

1. Purpose: Standardize the relevant personnel to set the furnace temperature curve correctly to ensure the quality of SMT products.

2. Scope: suitable for setting the temperature curve of lead solder paste from SMT manufacturers.

3. Responsibilities:

Engineering Department: Set the furnace temperature according to this procedure.

Quality Department: Check the furnace temperature setting according to this procedure.

4. Assignment content:

4.1 Test method: Determine the heat capacity category according to the product to be produced, and use the finished product provided by the customer or a blank temperature measuring board that matches it to test whether it meets the curve requirements of the corresponding category; if it meets the requirements, the actual veneer produced also meets 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 requirements of solder paste for temperature curve are as follows:

4.2.3 Requirements for components: The set temperature must meet the requirements of the reflow profile of all SMD devices. Too high temperature can cause potential damage to the components; for relays, crystal oscillators and thermal devices, the temperature can meet the soldering requirements The lower limit.

4.2.4 Layout and packaging of components: mainly consider the form of device packaging. For single boards with high component density, as well as single boards with PLCC, BGA and other components with large heat absorption and poor thermal uniformity, the preheating time and The upper limit of the temperature is taken, and the two sides of the PCB must be divided into levels.

4.2.5 PCB thickness and material: the thicker the PCB, the longer it takes for soaking; for special materials, the heating conditions must be met, mainly the maximum temperature and duration that they can withstand during reflow.

4.2.6 Considerations for double-sided reflow process: For the double-sided reflow soldered board, first produce the side with a smaller overlap area between the component pad and the PCB pad. In the case of similar ratios, give priority to the production of the smaller number of components When setting the temperature of the second surface, in the recirculation zone, if there are components that are easy to fall on the first surface, there should be a 5-10 degree difference between the upper and lower temperature settings.

4.2.7 Requirements for production capacity: When the chain speed setting of the reflow furnace becomes the bottleneck of production, increase the chain speed or increase the temperature of the heating zone (the wind speed remains unchanged) to meet the production requirements.

4.2.8 Factors of equipment: heating method, length of heating zone, exhaust gas emission, and the flow rate of intake air affect the return flow.

4.2.9 Principle of the lower limit: On the premise of meeting the welding requirements, in order to reduce the temperature damage to the components and PCB, the lower limit of the temperature should be taken off.

4.2 IPQC compares the actual measurement curve according to the requirements of the reflow oven curve to check whether it meets the specified requirements.

5. Matters needing attention:

5.1 The temperature settings of each temperature zone above are only reference settings. The specific temperature settings should be determined according to the condition of the reflow oven and the solder paste model, but the temperature curve actually tested should meet the requirements of the above temperature curve.

5.2 SMT patch processing: When continuously producing the same product, measure the furnace temperature curve once per shift; test the furnace temperature curve once before the trial production of the new product and before the transfer, and the temperature setting should not be changed casually. (Except for special requirements of customers).