SMT solder paste and red glue process overview
Red glue process:
The SMT red glue process takes advantage of the hot curing properties of the red glue, which is filled between two pads by a press or dispenser, and then cured by patch and reflow welding. Finally, through wave soldering, only the surface mount surface over the wave crest, without the use of fixtures to complete the welding process.
SMT solder paste:
SMT solder paste process is a kind of welding process in surface mount technology, which is mainly used in the welding of electronic components. SMT solder paste is composed of metallic tin powder, flux and adhesive, which can provide good welding performance and ensure reliable connection between electronic devices and printed circuit board (PCB).
Application of red glue process in SMT:
1.Save Cost
A major advantage of the SMT red glue process is that there is no need to make fixtures during wave soldering, thus reducing the cost of making fixtures. Therefore, in order to save costs, some customers who place small orders usually require PCBA processing manufacturers to adopt the red glue process. However, as a relatively backward welding process, PCBA processing plants are usually reluctant to adopt the red glue process. This is because the red glue process needs to meet specific conditions to be used, and the welding quality is not as good as the solder paste welding process.
2.The component size is large and the spacing is wide
In wave soldering, the side of the surface-mounted component is generally selected over the crest, and the side of the plug-in is above. If the surface mount component size is too small, the spacing is too narrow, then the solder paste will be connected when the peak is tinned, resulting in short circuit. Therefore, when using the red glue process, it is necessary to ensure that the size of the components is large enough, and the spacing should not be too small.
SMT solder paste and red glue process difference:
1. Process Angle
When the dispensing process is used, the red glue will become the bottleneck of the entire SMT patch processing line in the case of more points; When the printing process is used, it requires the first AI and then the patch, and the precision of the printing position is very high. In contrast, the solder paste process requires the use of furnace brackets.
2. Quality Angle
Red glue is easy to drop parts for cylindrical or vitreous packages, and under the influence of storage conditions, red rubber plates are more susceptible to moisture, resulting in the loss of parts. In addition, compared with solder paste, the defect rate of red rubber plate after wave soldering is higher, and typical problems include missing welding.
3. Manufacturing cost
The furnace bracket in the solder paste process is a larger investment, and the solder on the solder joint is more expensive than the solder paste. In contrast, glue is a special cost in the red glue process. When choosing the red glue process or solder paste process, the following principles are generally followed:
● When there are more SMT components and fewer plug-in components, many SMT patch manufacturers usually use solder paste process, and plug-in components use post-processing welding;
● When there are more plug-in components and less SMD components, the red glue process is generally used, and the plug-in components are also post-processed and welded. No matter which process is used, the purpose is to increase production. However, in contrast, the solder paste process has a low defect rate, but the yield is also relatively low.
In the mixed process of SMT and DIP, in order to avoid the double furnace situation of single-side reflux and wave crest, red glue is placed on the waist of the chip element on the wave crest welding surface of the PCB, so that tin can be applied once during the wave crest welding, eliminating the solder paste printing process.
In addition, the red glue generally plays a fixed and auxiliary role, and the solder paste is the real welding role. Red glue does not conduct electricity, while solder paste does. In terms of the temperature of the reflow welding machine, the temperature of the red glue is relatively low, and it also requires wave soldering to complete the welding, while the temperature of the solder paste is relatively high.