What is DFM Manufacturability AnalysisYYfab'Circuits

1. What is DFM? DFM manufacturability analysis is actually a bridge between R&D and production, communicating between them, and  to mak e  better products at a lower cost by simplifying , optimizing , and improving product design DFM manufacturability analysis means that manufacturability is considered from the time of product development and design, so that design and manufacturing are closely linked, to achieve the goal of succe ss  from design to manufacture  without any problem . The specific situations are as follows: Identify potential problems during the design phase and provide solutions Component design error avoidance Make appropriate component substitutions if any chance to improve component quality or reduce costs while meeting the original needs Improve the productivity in production processes and component quality Reduce the cost of product production 2. Why is DFM so important? The goal of the enterprise : low cost , high output , good supply capacity , and long-term reliable products . That means to produce better products with less money, and DFM can meet the needs from enterprises to a large extent. DFM is critical for efficiency, speed and high productivity. Many people believe that about 70% of product manufacturing costs come from the initial design stage, such as materials or manufacturing, so DFM has a great ability to reduce costs. In addition, DFM can also play a role in the entire manufacturing and production process. The influence map of each cycle of the p r oduct (from the Internet) Here are a few specific points: With DFM, production costs can be reduced Accelerate the time to market Reduce development costs Reduce the number of revisions or do not require revisions, reducing development costs Reduce rework and rework costs Find errors and glitches, and avoid them Provide a higher quality product as the design can be improved and enhanced at each stage   From the perspective of engineers, DFM manufacturability analysis saves engineers a lot of trouble. No need to be urged by the boss, no need to stay up late to change the board, no need to bear the pressure of many parties, and can also reduce the number of times been  bullied. Application of DFM in each stage of product 3. What would happen without DFM? In order to assemble printed circuit boards as quickly and efficiently as possible, it is important to design according to DFM requirements. Here are a few common problems that may arise if DFM manufacturability analysis is not performed. Importance of DFMs Haven ’ t done a better choice for material price and availability The price of electronic components may vary depending on the channel , which may have an unexpected impact on PCB assembly. Although this has little impact on the sample cost, once it is put into production, the cost will rise rapidly . For example: if you spend $1 more on electronic components that have been used 10 times in the design, you can ignore adding $1 to one board, but if it is 10,000 boards, it will be $10,000. If all the components on the PCBA are considered, the difference of $1 will also generate a huge cost difference. This is just a example, but in more cases, the board may be far more than 10,000 pieces. Of course, not only the price, different suppliers and distributors will also have different changes in the application of components . If the price of the material is low, but it is not available during   production, it may face huge manufacturing delays. Especially at the end of the product production cycle , if the material is marked as not meeting the new design, service life is not up to standard, or obsolete, it is necessary to redesign the circuit board to adapt to the updated  material , and may have to stay up all night to change the board . patch map PCBA assembly failed If the material does not match the PCB, it will cause many errors in the manufacturing process. Here are a few common ones: B ad solder joint Components that are not properly rotated for wave soldering can create bad solder joints, which may happen to the via holes and surface mounted(SMT) components. The position of components is also important, because some components may prevent good solder from being used to the other parts, causing worse connection. Solder Bridge Surface mounted pins that are very close may have a thin strip of solder between them. These solder strips may cause intermittent shorts that are difficult to find and correct. Tombstone Discrete SMT parts that are thermally unbalanced between their pins may have problems going through a reflow oven, this imbalance can pull out one of the pins and pull the part up until it stands upright like a tombstone. Floating Parts If the pad size is wrong, reflow SMT components may float misaligned, which may cause interference with other circuits Of course, here are just a few, in fact there will be more problems, any materials that cannot be matched correctly may need to be manually soldered or even redesigned, which means slowing down the manufacturing speed of the circuit board and spending more time and money.   Tin dipping chart of gold finger (picture comes from the Internet) Reliability design Designing for reliability is also a common problem where circuits are designed without consideration for PCB assembly and practicability. Assuming that the product is used outdoors, it must be resistant to high temperature, but it was not considered at all during the design. Such a product did not meet the standard at all during the test, and then began to redesign, select materials, and other questions   may appear in subsequent production. Manual welding component diagram 4. How to apply DFM in product production? Start with the schematic diagram When designing the schematic diagram, the designer will choose the required materials , usually based on the function to be realized, but many other factors must also be considered, including the price , reliability and life cycle of the material . If you start thinking about it at the design stage, it will save a lot of trouble, and avoid the trouble of the manufacturer. Here I have to talk about BOM. There are many matching materials on the market, which can actually solve a lot of problems.While there will be a little bit trouble when it comes to the production stopped, you need to consider the alternative selection.   schematic diagram PCB layout PCB layout is also an important part of design, and in the early stages of design, important decisions about how to set up the board also directly affect how the board is manufactured.  Single-layer board, double-layer board or multi-layer board? Two-layer boards are usually  used for signal integrity and thermal management , while also considering the manufacturability of the board . For example, determining the board thickness required for the vias used with the optimum drill aspect ratio, which requires using a different board material or changing the number of layers of the board. Circuit Board model outline Determine the model and outline of the PCB, requiring detailed circuit board shape and size , including placing fixed components, through holes , slots , etc. Care must be taken here so that redesign and assembly errors can be avoided. Materials To avoid soldering problems during assembly , it is necessary to have the materials ready. Place and route according to DFM requirements PCB component placement and routing requires layout with the shortest signal paths in high-speed and power circuits for best electrical performance. When laying out a board , it is important for the PCB designer to strike a balance between the electrical and manufacturing needs of the board . Mainly pay attention to the following points: Points to note Description SMT In order make the chip mounter automatically assemble components, it is necessary to keep a certain distance between the components. Of course, manual soldering cannot be avoided sometimes.   Wave soldering Both the DIP and SMT components need to be placed perpendicular to the direction of the circuit board through the solder wave, which is conducive to the even distribution of solder around the component pins. The placement of the DIP components will also affect the solder. For example, when the DIP and SMT components are on the same side of the PCB, reflow soldering will be performed before wave soldering. Reflow soldering The two pins of a smaller discrete SMT part need to be thermally balanced for reflow soldering. When a pad is connected to large area metal, it can act as a heat sink and cause the solder paste on that pad to reflow more slowly than the other pad, causing part tombstoning. Pad size is also a problem, as pads that are too large may cause parts to float out of alignment, while pads that are too small may not hold enough solder paste to reflow into a solid connection.   PCB Package Vias that are too large for their pins can scatter solder through them too quickly, resulting in poor solder connections. SMT pads that are too large may contain too much solder paste, which can bridge to adjacent pads and cause shorts. Pads that are too close together are also prone to solder bridging. This often occurs in fine pitch components where there is not enough solder layer between pads to prevent bridging.       Design finalization and documentation In addition to place and route, there are many other tasks during PCB layout that affect board manufacturability: Points to note Description PCB Testing To verify the accuracy of the assembly process, circuit boards often include test points accessible to the probes of the test fixture. However, if test points were not included in the original design, the board must be redesigned to add them before it can go into production. A redesign like this is not only costly and time consuming, but it may also generate new DFM issues that didn't exist before. Silkscreen and PCB marking Silkscreen marking is important for PCB testing, rework and debugging. If the necessary information is not on the board, manufacturing can be slowed down,meanwhile rework and testing technicians need to look for specific parts or polarity markings. Design summary drawing Without complete and accurate information on design revisions, time may be wasted when verifying manufacturing details, or even worse, errors can be made during board production.      

How to choose proper solder paste during PCB assemblyYYfab'Circuits

Devil is in the detail, choosing solder paste may seem like a trivial matter, but actually solder paste can make or break the PCB assembly process. There are all kinds of solder pastes to choose from on the market, while it doesn't look like that much of difference based on the classification, not all solder pastes are created equal. Specialty solder pastes are generally more expensive, but often have additional benefits. Choosing the right solder paste will avoid many problems. Many factors influence solder paste selection, such as: wetting characteristics, void control, flux residue, alloy strength, alloy flexibility, and other performance metrics. Changes in these performance indicators will affect the selection of solder paste. For example: Quality can be maximized by choosing a slurry that performs best with the material, geometry and heating process used to manufacture the product. Throughputcan be maximized by selecting a solder product for optimal deposition and heating methods . Cost targets depend on quality and yield, and can be maximized by considering material, direct labor, inspection, rework, and scrap values. Here are some factors to consider when choosing the right solder paste. 1.Leaded or lead-free solder paste The biggest difference between l eaded and lead -free is toxic and non-toxic , and the other is the melting temperature . Lead-free solder paste has a higher melting point. Here you can choose according to the actual requirement. Regarding leaded and lead-free solder paste, there is a detailed summary in the previous article, you can click on the title to jump directly. Leaded solder (left) and lead-free solder (right) 2.Water-soluble or no-clean solder paste? Water-soluble solder pastes contain high-molecular compounds, such as polymers, which are not as effective as rosin/resin in preventing re-oxidation . After the board goes through the reflow stage, the water-soluble solder paste gives the board a cleaner look, with the flux residue burned off and easily washed off in a board washer. No-clean pastes function is the same as water-based pastes, but residues are left on the board . No-clean chemistries are typically rosin/resin based materials. The rosin/resin could forms an excellent oxide barrier and protects the "clean" surface from re-oxidation during reflow, where aesthetics can suffer. The specific ones can be selected according to actual requirements. 3.Melting point temperature of solder paste Shown as below picture, each alloy has a temperature at which it changes from solid to liquid , as shown in the diagram below . The phase transition from solid to liquid begins when the solidus is reached and ends when the liquidus is reached . Below the solidus line, the alloy is 100% in the solid state. Between the solidus and liquidus, a region known as the plastic range, some parts of the alloy are solid but mostly liquid. When the solidus and liquidus are equal, the alloy is called a eutectic alloy. Although wetting begins at the solidus temperature, optimal wetting is achieved at 15º C higher above the liquidus or higher peak temperatures. If the solder joint needs to maintain physical integrity during a subsequent operation (such as a second reflow process), the peak temperature of the subsequent operation needs to be below the solidus temperature of the alloy. Melting point temperature of solder paste 4.Alloy composition Generally , you can choose Sn63 or Pb37 solderalloy composition , which can match the soldering requirements. For Ag or Pd plated products, you can choose Sn62 or Pb36 or Ag2 solder paste. For products without thermal shock , you can choose solder powders containing bismuth . Alloy Composition Solder Paste Selection 5.Particle size (mesh number) Also known as particle size, it refers to the number of meshes per square inch; in the actual tin powder production process, most tin powders are collected with several layers of sieves with different meshes, because the mesh size of each layer of sieves is different, so the grid of the particle size of the tin powder in each layer is also different, and the particle size of the finally collected tin powder particles is also a regional value. Particle Size Map of Solder Paste Therefore, the larger the mesh number of the solder paste is, the smaller the particle size of the tin powder in the solder paste will be; the smaller the mesh number is, the larger the particle size of the tin powder in the solder paste will be. That is, when the solder paste manufacturer selects the solder paste according to its mesh index, it should be determined according to the distance between the solder joints with the smallest distance on the PCB: if there is a larger distance, you can choose the solder paste with a smaller mesh size . Conversely, when the spacing between solder joints is small, solder paste with a larger mesh size should be used, and the general particle size is about 1/5 of the opening of the SMT stencil. 6.Viscosity In SMT workflow, from laser stencil printing (or spotting) of solder paste to attaching components to the reflow heating process, there is a process of moving, placing or carrying the PCB; To ensure solder paste not deformed, and the components attached to the PCB solder paste are not displaced. It is required that the solder paste should have good viscosity and hold time before the PCB enters reflow soldering heating . Among them, 200-600Pa·S solder paste is more suitable for needle-type or highly automated production process equipment; the printing process has relatively high requirements for the viscosity of solder paste, so the viscosity of solder paste used in the printing process is generally around 600-1200Pa·S . Suitable for manual or mechanical patch screen printing. High-viscosity solder paste has the characteristics of good solder joint accumulation effect , and is more suitable for small-pitch printing ; The low-viscosity solder paste has the characteristics of fast falling speed, tool-free cleaning, and time-saving printing ; Reminder: The viscosity of the solder paste will change with the stirring of the solder paste, and the viscosity will decrease when stirring; stop stirring, and the viscosity will return to the original state; this is very important for how to choose different viscosities. Solder paste plays a very important role. In addition, the viscosity of solder paste has a great relationship with temperature. Under normal circumstances, its viscosity will gradually decrease with the increase of temperature. 7.Storage stability We need the solder paste to have a stable quality , but in practical applications, the stability of the solder paste will change from purchase to storage and storage for a period of time. 8.Printing stability In the actual production process, the performance of reflow soldering is also very important, which has a great influence on the quality . 9.The final effect of soldering It mainly includes the following four aspects: good wettability, less BGA fusion and poor fusion, preheating collapse, and recovery ability after printing stop. Solder wetting is part of the process by which the metal in the solder bonds with the metal on the printed circuit board (PCB) or component . In a comparison with different solder pastes, you will find that A is more wetting than B. Comparison Between Different Solder Pastes In the BGA process, due to limited conditions, the fusion ability of solder paste is more important. The higher the degree of preheating collapse, the lower the incidence of poor bridging. You can find that there is no collapse in the left picture, that is, 0.3mm/0.2mm, but there is a collapse in the right picture, that is, 0.4mm/0.3mm. Excellent shutdown recovery can improve printing production efficiency to a certain extent. From this photo, you can see the difference curve after stopping for an hour. To sum up, we can know that choosing the right solder paste should not only consider the characteristics of the solder paste itself and its impact on quality and production, but also consider various factors in mass production . Therefore, it is necessary for us to continuously record and summarize the impact of solder paste from various suppliers on products in actual production.