Factors affecting reflow soldering process and floating height

1. Generally, PLCC and QFP have larger heat capacity than a discrete sheet element, and it is more difficult to weld large-area components than small components.

2. In the reflow furnace, the conveyor belt makes the conveying products reflow again and again. At the same time, it also becomes a heat dissipation system. In addition, the heat dissipation conditions between the edge and the center of the heating part are different, the edge temperature is generally low, and the temperature of the same carrier surface is also different in addition to the temperature requirements of each temperature zone in the furnace.

3. Different effects of product loading. The adjustment of temperature curve of reflow soldering should consider that good repeatability can be obtained under no-load, load and different load factors. Load factor is defined as: LF = L / (L + s); Where l = length of assembled base plate and S = interval of assembled base plate. The larger the load factor, the more difficult the reflow process is to obtain good repeatability. Generally, the maximum load factor of reflow furnace is in the range of 0.5 ~ 0.9. This depends on the product conditions (component welding density, different substrates) and different models of the reflow furnace. To get good welding effect and repeatability, practical experience is very important.

How to solve the problem of component floating height after reflow soldering of SMT red glue?

After the red glue is cured by reflow soldering, if the mounting element floats, it may be due to:

(1) The heating rate is too fast and the red glue expands too much;

(2) Too many bubbles in red glue;

(3) When reflow soldering mounted components, the position of the patch is set improperly.

1. With reference to the ipc610c standard, everything is subject to the customer's standard, and the customer's "satisfaction" is the final standard.

2. Glue quality: use and storage (keep it in the refrigerator, remember it seems to be 0 ~ 4 degrees, check the glue description, and ask the supplier if there is no need) pay attention to that the gasification process of reflux after moisture is easy to lead to the offset and floating of components; Too much glue is hard to control; The reflow curve refers to the requirements of glue reflow. The supplier didn't ask for it. The supplier didn't have the glue too much. It wasn't made professionally.

3. The temperature setting of reflow furnace is the same as above. In addition, the reflow wind speed also has an impact, mainly on the influence of element offset and floating height. In addition, pay attention to the constant temperature before 100 degrees. Personally, I think it will be affected by the gasification of tide. Lengthen the constant temperature time before 100 degrees to reduce the influence of violent gasification of water; It is recommended to adopt the curve of slow heating constant temperature curing cooling.