PCB splicing is to combine several small PCB units with various connection methods. The more common Mosaic has AA sequence spelling, AB positive and negative spelling, AA rotation spelling, AB yin-yang spelling, ABC mixed spelling and so on. PCB design engineers usually take into account the structural size, electrical performance, component layout and other functional aspects of the product when designing the board. In the aspect of panel design, how to improve the SMT production efficiency and minimize the impact on product quality risk, encountered in the PCBA production process, such as the irregular PCB shape size, after the assembly affects the production efficiency, and it also increases the production difficulty and manufacturing costs.
PCB assembly purpose: a. Due to the small size of PCB, irregular seriously affect the SMT processing production efficiency. b. Maximize board utilization and reduce costs. c. Reduce the difficulty of production and improve the yield of products.
There are many ways to design panels, and it is sometimes difficult to determine which type of panels and the optimal number of panels are used in the trial production stage of new products. PCB design engineers according to product characteristics (such as product structure limit, peripheral interface limit, limit and other factors) in the design of priority to meet the structural requirements of the product, followed by the PCB board and SMT processing process feedback board utilization and production efficiency issues. After the PCB board is selected in the production process, the different geometric sizes and the thermal expansion after the furnace of the PCB board directly affect the reliability and performance of the product, and increase the processing difficulty and manufacturing cost of SMT production. Combined with the experience of SMT process engineers for many years, the adoption of a patchwork approach to improve the efficiency of SMT production lines, there are the following aspects to share with you:
In order to improve the operation rate of the production line in the SMT production line, there are two common ways of assembling AAAA or AB, we can not directly ask which kind of assembling method is good? This should be considered from the process complexity of the product, the balance rate of the machine mounting cycle of the production line after the assembly, the problem of falling parts after the secondary remelting of large components, and so on.
The advantage of AABB is that SMT production line equipment configuration and process flow are simple and easy. A steel mesh, a set of SMT program and SPI/AOI inspection program and reflow welding furnace temperature curve optimization, etc., improve the SMT fast line change speed and the first part check once completed, in a very short time PCBA finished product output to the next process functional testing.
The disadvantage of AABB is that if the BOT surface and the TOP surface of the product have a large difference in component layout (the main chip size is large, the component layout density is high, the through-hole return element foot exceeds the board surface, etc.), the solder paste in the fine-pitch position will be poorly printed and unstable, and the components with large volume and weight will be at risk of falling off during the secondary furnace. In mass production, not only does it not solve the problem of efficiency improvement, but also brings processing difficulty and quality problems, which is also a test of engineers' online technical research ability.
(AAA/BBB) non-positive and negative design, more suitable for most factory recommendations, easy deployment of production lines and reasonable arrangement of equipment resources, stable production process, it is easy to improve the efficiency of the production line. In PCB design, engineers must consider the overall main chip components, large heat dissipation components, and peripheral interface components layout rationality, processing plants only need to reasonably arrange the production line to produce BOT surface (less component surface) and then produce TOP surface (multiple parts surface), and process engineering is easier to deal with when quality anomalies are encountered in the processing process.
In the production process to ensure the straight-through rate under the premise of what is the best way to use? It is necessary to comprehensively consider the machine configuration of the SMT production line and the processing capacity of the equipment, process stability and other factors.
1. First of all, familiarize yourself with SMT production line configuration and theoretical capacity:
Production line PCB maximum size :774mm*710mm, NXT can be attached to the minimum package 03015, 01005 components, NXT module theoretical capacity of 35,000 components /H, AIM multi-function machine theoretical capacity of 27000 components /H.
2. The single-side SMT process of a product of SMT is 6 pieces, and the original 6 pieces are optimized to 12 pieces when mounting, reducing the number of plate passing and cycle frequency to improve production capacity.
3. SMT machine configuration of each line body is different, equipment engineers balance the speed of each machine when changing the line, printing press, SPI solder paste detection speed, patch speed, reflux furnace speed and AOI detection speed after the furnace, optimize the entire production line fully automated high-speed production, greatly improve the machine utilization efficiency.
In the case of high quality and few personnel, efficient output is our goal of pursuing and continuous improvement. For small and medium-sized batches and the development and proofing stage of PCB is a variety of, in order to meet the high efficiency of the SMT machine per hour output, in the PCB assembly is a very important link:
The board size is less than 80mm on any side, and the maximum size of the PCB after the board is assembled (L)300-350mm * (W)200-250mm is more appropriate.
When the outline of the connector with the edge between the plates exceeds the interference, it is solved by the rotary combination + process edge method to prevent the poor quality of the collision damage during the transmission or handling after welding.
When the hollow-out area of some irregular shape PCB is large, it is easy to lead to the wrong identification of the PCB sensor on the equipment transmission track during SMT production, resulting in wrong action or not sensing the PCB stacking phenomenon, and the hollow-out position is completed by adding the process edge during the board design.
After the board design, it must be ensured that the edge of the reference point of the large board is less than 3.5mm from the edge of the board (the minimum range of the machine in the clamping PCB board edge is 3.5mm), the two diagonal reference points on the large board can not be placed symmetrically, and the reference points on the front and back are not placed symmetrically, so that the reverse/reverse PCB can be prevented from entering the machine through the identification function of the equipment itself.
In the process of panel design, the number of connection points and placement positions between boards are also very important.
All in all, in order to meet the board utilization rate and production and processing efficiency, the panel design should also consider the PCBA thermal deformation and panel efficiency after production.
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