QA sampling criteria and quality definition methods in SMT QA sampling criteria and quality definition method in SMT A customer complaints (20%) 1 no complaints and any serious feedback in the month, full marks. 2 1 case of complaints in the month deducted 10 points, 2 cases of complaints 0 points Discipline (15%) 1 No violation of company labor discipline, full marks. 2 Unexcused lateness and early departure deduct 5 points 3 without authorization, unauthorized absence from work deducted 5 points 4 work to do things unrelated to work deduct 5 points Three line management (15%) 1 to meet the requirements of the program documents, without any adverse items, full marks 2 does not meet the requirements of the program documents, random audit found a bad project deduct 5 points Work efficiency (10%) 1 timely and accurately complete the reasonable tasks explained by the supervisor, full marks 2 unexplained inability to complete the reasonable tasks of the supervisor, are deducted from 5 points V. Team spirit (10%) 1 Be able to take the initiative to help new employees, assist others/other departments to complete the task, full marks 2. 5 points will be deducted for failure to cooperate with reasonable requests for assistance from supervisors or other departments. Communication and presentation skills (10%) 1 If a problem is reported and communicated in a timely manner, and if the problem is reflected in a clear and understandable manner, full marks. 2 5 points will be deducted for failing to report and communicate problems in a timely manner. 3 5 points will be deducted if there is a serious discrepancy between the problem and the actual situation. VII 5s (10%) 1 Correct use and maintenance of equipment, reports and records are clear, full marks. 2 Damage to instruments and equipment, stationery/tools are not returned to their place, 5 points will be deducted. 3. 5 points will be deducted if the report is not filled out in time, not clear, or if it is not signed or altered. Pass rate (10%) 1 Individuals with products monthly pass rate ≥ 99.5%, full marks 2 Personal products monthly pass rate ∠ 99.5%. 0 points. The definition standard of QA and the quality definition standard in SMT have been introduced.

Six Sigma Definition Six Sigma a.k.a.: 6σ, 6Sigma, 6Σ Sigma (Σ, σ)[1][2] is a Greek letter that is a statistical unit used to measure the standard error in a total number. Its meaning is derived to mean that the defect rate of an average company is about 3 to 4 sigma, which, in terms of 4 sigma, is equivalent to 6,210 errors per million opportunities. If a company continually pursues quality improvement to the extent that it reaches 6 sigma, its performance will be close** to meeting customer requirements, with only 3.4 defective items found out of a million opportunities. The Six Sigma (6σ) concept, as a quality management concept, was first proposed by Bill of Motorola in 1986, with the aim of designing a goal: to reduce the number of defects in products and processes in the production process, to prevent product variation, and to improve quality. Really popular and developed, is the practice of General Electric Company, that is, the 1990s developed 6 σ (sigma) management is summarized in the successful experience of quality management, distilled the essence of which the process management skills and * proven methods, to become a kind of management model to improve corporate performance and competitiveness. The management method in Motorola, General Electric, Dell, Hewlett-Packard, Siemens, Sony, Toshiba and many other multinational enterprises has proved to be fruitful. For this reason, some domestic departments and organizations vigorously push 6σ management in domestic enterprises and guide them to carry out 6σ management. With the accumulation of practical experience, it has been derived from a mere process optimization concept to a management philosophy. It is not only a standard to measure the capability of business processes, not only a set of methods for continuous optimization of business processes. The Greek letter σ (pronounced SIGMA, capitalized as Σ) is a unit in statistics that represents the standard deviation from the mean. The Six Sigma (SIXSIGMA) quality level indicates that there are only 3.4 defects in a million opportunities for defects in a production or service process, i.e. a pass rate of 99.9997% is achieved. The implementation of Six Sigma quality plan requires management intervention, and by specially trained internal Six Sigma quality plan staff and project leaders to organize and implement, in order to achieve the short-term goal of reducing deviations and improving process capability and the long-term goal of achieving the world** level of Six Sigma. Six Sigma is the enterprise to refine the scientific management of a quality goal, this quality goal is the enterprise within the various departments to work together to be able to achieve the overall. Motorola and General Electric and other companies to implement the achievements of Six Sigma, but also within the business sector hundreds of thousands of impact on product design, production, service, one by one to improve the results of efforts. The Six Sigma approach has affected dozens of management processes and transaction flows. For example, in customer support and product delivery, a better understanding of customer needs and improvements in evaluation systems have enabled us to take greater strides in pursuing service improvements and timely product delivery.

The three main elements that determine the quality of SMT screen printing In SMT, a typical PCB (Printed Circuit Board) may have several hundred components and 600 to 1,000 coupling points (i.e. pad pads) on it. The solder failure rate at these endpoints must therefore be kept to a minimum. In general, 60% of PCBs that fail testing and have to be reworked are due to poor solderpaste silkscreen quality.    Below, we will discuss the fundamentals of screenprinting and explore the techniques required to consistently ** screenprint quality in production.    There are three key elements in solder paste screen printing, here called the three S's: Solderpaste, Stencils, and Squeegees. The right combination of these three elements is the key to consistent screen quality.    Elements that determine the quality of SMT screen printing I: Solder Paste (the first S)   Solder paste is a combination of solder beads and rosin, the function of which is to remove oxides from component pins, pads and beads during the first stage of reflowing in the soldering oven, which lasts about three minutes at 150°C. (Resin is sometimes called rosin. (Resin is sometimes called rosin, and technically, resin is a natural product while rosin is man-made.) Solder is an alloy of lead, tin and silver that is reflowed in the reflow oven** at about 220°C. The silver and rosin both play a role in helping to melt the solder. Both silver and rosin play a role in helping to melt the solder and wetting to achieve reflow, i.e. the role of the flux. (Wetting: is a descriptive term for the effect of soldering, where the object being soldered appears to be "wetted" by the tin.)    Spherical solder particles are manufactured into a variety of mixed sizes, and then screened and graded. Solder paste is graded according to the size of the beads, as follows:    Type 2: 75-53mm    Type 3: 53-38mm    Type 4: 38-25mm (m=micron=0.001mm) The Law of Three Balls    The Law of Three Balls gives production a simple formula for selecting a silkscreen stencil; the size of the solder bead in the solder paste must match the silkscreen stencil, as described below:    Empirical formula:    At least three *large diameter tin beads can be lined up vertically in the thickness direction of the screen printing stencil.    At least three *large diameter beads can be aligned horizontally across the width of the *small holes in the screen printing template.   The calculation is slightly more complicated because the beads are measured in metric microns (m), while the industry standard for the thickness of screen printing templates is the US-specific unit thou!    (1mm=1x10-3mm,1thou=1x10-3inches,25mm?1thou.)    Solder Paste Type 3x*Large Bead Size *Close Stencil Thickness    Type 2: 75-53m 3x75m=225m=9.0thou 9 thou    Type 3: 53-38m 3x53m=159m=6.4 thou 6 thou    Type 4: 38-25m 3x38m=114m=4.6 thou 4 thou   The size of the silk-screened hole is determined by the component pin spacing (pitch), and the size of the pad is generally half the pin spacing. (The size of the silkscreen hole may actually be a little smaller than the size of the pad.) For example, for a 25 thou (0.63mm) spacing, the silkscreen hole is 12.5 thou. Therefore, the solder paste must be selected to meet the *smallest* silkscreen hole on the silkscreen stencil:    Component *Small pin spacing *Small silkscreen hole Suitable solder paste type    16 thou 8 thou Type 2: 75-53m    12 thou 6 thou Type 3: 53-38m    8 thou 4 thou Type 4: 38-25m    Therefore, the thickness of the silkscreen stencil is usually the deciding factor, and for most applications the standard 6 thou thick silkscreen stencil with type 3 solder paste is selected. Viscosity   Viscosity is an important characteristic of solder paste, from the dynamic aspect, in the screen printing stroke, the lower its viscosity, the better the mobility, easy to flow into the screen printing holes, printed on the PCB pads. From the static side of the consideration, silk screen after scraping, solder paste stays in the silk screen hole, its viscosity is high, it maintains the shape of its filling, and will not collapse downward, which is more important for waiting for the patch before the silk screen in the pads of the solder paste.   The viscosity of the paste in its container tank is measured using a delicate and often expensive laboratory viscometer. Standard viscosities are in the range of about 500kcps-1200kcps, with a more typical 800kcps being ideal for stencil screen printing. A more practical and economical method of determining whether a solder paste has the correct viscosity is as follows:   Stir the paste with a spatula inside the container jar for about 30 seconds, then pick up some paste, three or four inches above the container jar, and let the paste drip down on its own; it should slide down like thick syrup at first, then break off in sections to fall into the container jar. If the paste can not slide down, it is too thick, if it has been falling with

Quality control knowledge of SMT stencil design I. General technical requirements    1, mesh frame: frame size according to the requirements of the printing machine, DEK265 and MPMUP 3000 models, for example, the frame size of 29ˊ 29ˊ, the use of aluminum alloy, frame profile specifications for 1.5ˊ 1.5ˊ. 　2, taut mesh: the use of red glue + aluminum tape way, in the aluminum frame and glue adhesive joints, must be evenly scraped with a layer of protective paint. At the same time, in order to ensure that the net plate has enough tension and good flatness, it is recommended that the stainless steel plate from the inside of the frame to retain 25mm-50mm. 　3, the reference point: according to the size and shape provided by the PCB information according to the 1:1 way openings, and in the printing of the reverse side of the engraved semi-transparent. In the corresponding coordinates, the whole PCB open at least two datum points. 　4, opening requirements: 　　Position and size to ensure a high degree of opening accuracy, strictly in accordance with the prescribed opening mode opening. 　　Independent opening size can not be too large, the width can not be greater than 2mm, pad size greater than 2mm in the middle of the need to set up a 0.4mm bridge, so as not to affect the strength of the stencil. 　　The opening area must be centered. 　5, characters: for the convenience of production, it is recommended that the lower left corner or lower right corner of the stencil engraved with the following characters: Model; T; Date; stencil production company name. 　6, stencil thickness: in order to ensure that the amount of solder paste printing and welding quality, stencil surface smooth and uniform, uniform thickness, stencil thickness refer to the above table, stencil thickness should be used to meet the * fine pitch QFP BGA as a prerequisite. 　　If there are 0.5mm QFP and CHIP 0402 components on the PCB, the thickness of the stencil is 0.12mm; 　　If there are 0.5mmQFP and CHIP 0603 components on the PCB, the thickness of the stencil is 0.15mm; II, the shape and size requirements of the opening of the printed tin mesh plate 　1, the general principle: 　　According to IPC-7525 stencil design guide requirements, in order to ensure that the solder paste can be smoothly released from the stencil openings to the PCB pads, in terms of stencil openings, mainly depends on three factors: 　　1,) area ratio / width to thickness ratio area ratio > 0.66 　　2,) mesh hole hole wall smooth. Especially for pitch less than 0.5mm QFP and CSP, the production process requires suppliers to make electropolishing treatment. 　　(3,) the printing surface as above, the mesh hole under the opening should be wider than the upper opening 0.01mm or 0.02mm, that is, the opening into an inverted cone, to facilitate the release of solder paste ineffective, while reducing the number of times the stencil can be cleaned. 　　Usually, the SMT components of its mesh plate opening size and shape and pads consistent with the 1:1 way to open. 　　Under special circumstances, some special SMT components, the size and shape of the stencil opening has special provisions. 　2 Special SMT components stencil opening 　　CHIP components: 　　CHIP components above 0603, in order to effectively prevent the generation of tin beads. 　　SOT89 components: due to larger pads and components 　　Pad spacing is small, easy to produce tin beads and other welding quality problems. 　　SOT252 components: due to SOT252 has a pad is very large, easy to produce tin beads, and reflow soldering tension caused by displacement. 　　IC: 　　A. For standard pad design, PITCH》=0.65mm的IC，the opening width is 90% of the pad width and the length is unchanged. 　　B. For standard pad design, PITCH "= 005mm IC, due to its PITCH is small, easy to produce bridging, stencil opening way length direction remains unchanged, opening width of 0.5PITCH, opening width of 0.25mm. Other cases: 　　A pad is too large, usually more than 4mm on one side, the other side is not less than 2.5mm, in order to prevent the generation of tin beads and displacement caused by tension, stencil openings are recommended to use a grid line division of the way, the grid line width of 0.5mm, grid size of 2mm, according to the size of the pads can be divided equally. 　　Printing glue stencil opening shape and size requirements: 　　For simple PCB assembly using the glue process, give priority to the use of dispensing, CHIP, MELF, SOT components through the stencil printing glue, IC will try to use dispensing to avoid stencil scraping. Here, only give CHIP, MELF, SOT printing and gluing stencil recommended opening size, opening shape. 　 1, stencil diagonal must open two diagonal positioning holes, select the FIDUCIAL MARK point openings.      2, the opening are long strip. 　Inspection methods 　　(1) Visually check the opening centered on the taut mesh leveling. 　　(2) Through the PCB entity to check the correctness of the opening of the stencil. 　　(3) wit