PCB design positioning reference symbols and dimensions

The fiducial markers (FiducialMarks) and the local fiducial markers are special PADs that the patch device uses for optical positioning. Benchmark Applications There are three applications for reference symbols, 1) full board positioning for PCBs; 2) positioning of PCB boards for imposition. 3) For the positioning of fine pitch devices, for this case, QFP with a pitch of less than 0.5 mm is recommended to set the positioning reference symbol at its diagonal position; the type of reference point (the type of Mark point reference point (Mark point). Number of fiducial points 1) Two global fiducial mark, located at the relative position of the diagonal of the PCB, and as far as possible away; 2) at least two fiducial marks on the board of each board, located on the diagonal of the PCB Location and try to stay away. The reference point design of the panel is designed to design at least one pair of benchmarks on each board; at least one pair of benchmarks is designed on the whole board (you can use the benchmark on the board without additional design); regardless of the reference point of the whole board or single The reference point of the board, the front and back sides of the board, the coordinates of the corresponding reference line relative to the lower left corner of the PCB board must be strictly consistent. Otherwise it will cause a patch error! As shown below. The best reference point mark for the shape and size of the reference is a solid circle. Dimensions and deviations: A=1.0mm±5%. There must be no other marks around the identification marks, such as conductors, soldering circuits, solder masks, etc. The empty area, the size of the empty area is larger than the outer size of the identification mark by 0.5 mm or more. Flatness: The surface flatness of the reference mark should be within 15 μm [0.0006"]. The position of the reference is most accurate, and the position of the reference point is preferably on the opposite side of the substrate. The farther the better, the reference point on the board should be at least 7.5mm from the edge of the printed board and meet the minimum reference point space requirement. The reference symbols are used in pairs. They are arranged at the opposite corner of the positioning element. The clearance of the reference must be around the reference mark and there should be an open area with no other circuit features or marks. The size of the open area must be equal to the radius of the mark. The entire plate reference point must meet the space requirement, alone The substrate is recommended to meet the requirements for the openness of the reference point. The reference material is gold plated, bare copper, nickel plated or tin plated, or solder coated (hot air uniform). There should be no other circuit features around the reference mark or Marked Clearance. Best performance when high contrast occurs between the fiducial mark and the substrate material of the printed board. localFiducial in mounted device When the number of pins is large and the lead pitch is ≤0.5mm, it is recommended to design a set of graphics for the optical positioning of a single device, that is, a local reference mark, which is recommended. SMT printed board vias and pads design SMT printed board Through Hole and Pad Design Pad Via 1) In principle, the via should be avoided as much as possible. 2) If a via is used on the pad, the smaller the via diameter, the better, and the via is completely filled. The via layout has no gap between the via and the pad which is not soldered. ≥0.3mm. If the via has been soldered, there is no requirement for the via to the pad. Note: The via may be due to capillary action. The molten solder is sucked away from the component, resulting in insufficient solder joints or solder joints. Unfilled vias can result in poor solder paste application and soldering. Four PCB pad design processes require pad design process requirements. The critical part of the design, the pad design is an extremely critical part of the PCB circuit design, because it determines the soldering position of the component on the printed board, determines the soldering position of the component on the printed board, and Reliable soldering process for solder joints Possible soldering defects, cleanability, properties, soldering defects that may occur during soldering, cleanability, measurable maintenance, etc. play an important role. Trial and visual inspection, maintenance, etc. play an important role. Considering component manufacturing errors, placement errors, and inspection and rework, considering component manufacturing tolerances, placement errors, and inspection and rework, the spacing between adjacent component pads is designed according to the following principles: The spacing between the device pads is required to be designed according to the following principles: IC component side Chip component frame Chip component ≥ 0.3mm IC component frame shielding cover ≥ 0.3mm ≥ 0.5mm ≥ 0.3mm ≥ 0.5mm ≥ 0.5mm ≥ 0.5mm Manufactured board edge ≥0.3mm Shield cover ≥0.5mm≥0.5mm≥0.5mm≥0.5mm Shaped component ≥0.5mm Distance ≥Discharge tube and adjacent component PAD ≥0.4mm Discharge tube and discharge tube The distance between the discharge tube and the discharge tube is ≥0.1mm. Description: Description: Component: Chip component: refers to components such as 0201, 0402, 0603, etc. Components: IC components: components such as BGA, QFP, QFN, aQFN, etc. Shaped component: different Element: headphone jack, side keys, battery connector, T card member; shield cover: shielding cover: refers to inner and outer edge of the shield cover pad. As long as the placement density allows, the above distance should be the maximum. As long as the placement density allows, the above distance should be the maximum. CHIP component pad design CHIP component pad design Chip component pad design should master the following key elements: Chip component pad design should master the following key elements: component pad design should master the following key elements a) symmetry - both ends of the solder The disc must be symmetrical to ensure a balanced surface tension of the molten solder. b) Pad Spacing - Ensure that the component ends or pins are properly mated to the pads. c) Remaining dimensions of the pad - the remaining dimensions after lap joint must ensure that the solder joint can form a meniscus. d) Pad width - should be substantially the same as the width of the component end or pin. 4. Side Flat Package Device (QFP) Pad Design Side Flat Package Device (QFP) Pitch Pad Width (mm) Pad Length (mm) 0.80.51.8 0.650.41.8 0.50.31.6 0.40.251.6 0.30.171.6 Square Flat No Pin-Plastic Package (PQFN) Five-Piece Flat Leadless Plastic Package (PQFN) Pad Design PQFN Conductive Pad Two Types of PQFN Conductive Pads 1) One that barely exposes the bottom side of the package, The other side of the bottom is encapsulated within the component. It is packaged inside the component. 2) Another type of pad has a portion exposed on the side of the package. 3) Design of large-area thermal pad ≈ The large-area exposed pad size of the device should also be considered to avoid the design of the large-area thermal pad, the large-area exposed pad size of the device, and the edge pad bridging. Edge pad bridging and other factors. 4) The conductive pads are similar in size to the pads around the device, but the pads are slightly extended to the periphery and the pads are similar in size to the periphery of the device, which is longer (0.3~0.5mm). Longer (0.3~0.5mm). IC and BGA pad design IC and BGA pad design BGA pad design: BGA pad design: pad design according to the nominal value provided by the supplier, the pad design is performed on this size; 1) according to the supplier Regarding the nominal value, the pad design is performed on the size; the pad surface treatment uses OSP to ensure the flatness of the mounting surface, OSP, and 2) the pad surface treatment uses OSP, which ensures the flatness of the mounting surface. Allow the component to be properly self-centering. Gold plating should be avoided because during reflow soldering, there is a self-alignment between the solder and the gold. Gold plating should be avoided because during reflow soldering, there will be a reaction between solder and gold, weakening the solder joint connection; weakening the solder joint connection; the via should not be on the pad as much as possible, such as the front and back sides. Holes and vias need to be plugged; 3) The vias should not be on the pads as much as possible. For example, if there are vias on the front and back sides, the vias should be plugged. If there is space between the pads, it is necessary to make a solder mask. Make a solder mask. 4) If there is space between the pads to make a solder mask, be sure to make a solder mask. BGA other requirements Other requirements: BGA other requirements: outline positioning line drawing method to be standard; 5) shape positioning line drawing method to be standard; when there are multiple BGABGA when arranging chip position, 6) when there are multiple BGAs, in When arranging the chip position, it is necessary to consider the processability; considering the repairability, usually about 1mm or more around the BGA; recommended) 1mm or more around the BGA 7) Considering the repairability, usually about 1mm above the BGA; (Recommended) For the lead pitch ≤0.5mm QFP and ball pitch 0.5mm BGA package device and ball pitch ≤ packaged device, 8) For QFP with lead pitch ≤0.5mm and BGA package with ball pitch ≤0.5mm, in order to improve the precision of the chip, it is required The IC sets the reference point at two diagonals. The chip precision requires that the reference point be set at both diagonals of the IC. IC two diagonally set the reference point 0.5mmPitchBGA Pad 1) The pad center of each solder ball on the PCB matches the center of the pad on each solder ball and the center of the corresponding ball of the BGA bottom; the corresponding solder at the bottom The center of the ball is matched; the center of the pad on each solder ball coincides with the center of the corresponding solder ball at the bottom; 2) The PCB land pattern is a solid circle, and the via hole cannot be processed on the pad; the land pattern is a solid circle The pad pattern is a solid circular via that cannot be processed on the pad; the maximum diameter of the pad is equal to the pad diameter of the BGA bottom solder ball; (recommended) the bottom solder ball pad diameter; recommended) The minimum diameter of the pad diameter b of the bottom solder ball is equal to the minimum diameter equal to the BGA bottom pad diameter minus the placement accuracy. (Recommended) The bottom pad diameter minus the placement accuracy. Recommended) Bottom pad diameter minus placement accuracy For example: bottom pad diameter is 0.3mm, mounting accuracy is ±0.05mm, PCB soldering is as follows: BGA bottom pad diameter is bottom pad diameter, mounting accuracy is ± The minimum diameter of the pad is 0.30mm-0.05mm. (The pad diameter of the bottom solder ball of the BGA device is based on the minimum diameter of the disk. (The pad diameter of the solder ball at the bottom of the device is based on the information provided by the supplier.) 3) The solder mask size is larger than the pad size. 0.15mm. The solder mask size is 0.1~ larger than the pad size. Pad diameter of aQFN (MT6253) with a ball diameter of 0.45mmPitch & 0.27mm ball diameter is recommended to be 0.27mm. The size of the solder mask window is recommended to be 0.37-0.4mm. . The fine pitch PAD of the fine pitch IC increases the copper skin and increases the attractive force of the side pins, which facilitates self-alignment of reflow soldering and prevents it from being soldered. J-shaped pin small outline integrated circuit (SOJ) and plastic chip pinned carrier (PLCC) soldered pin small outline integrated circuit (shaped pin small outline integrated circuit) and plastic chipped chip carrier () design The pins of SOJ and PLCC are J-shaped, the typical pin center distance is 1.27mm; a) single pin pad design (0.50~0.80mm) × (1.85~2.15mm); b) pin center should be soldered 1/3 of the inner side of the disc pattern to the center of the pad; c) the distance between the SOJ and the two rows of pads (the outline of the land pattern) A value is generally 5, 6.2, 7.4, 8.8 (mm); d) PLCCPLCC The distance between the outer contours of the two rows of pads: J=C+K (unit mm): J-pad pattern outline distance; KeyPad design KeyPad design KeyPad requires in principle: KeyPad requires in principle: in principle Try to design a complete concentric circle, and there must be no mechanical holes; 1) try to design a complete concentric circle, and there must be no mechanical holes; the diameter of each concentric circle should not be less than φ5mmφ5mm; 2) each concentric circle The diameter should not be less than φ5mm; the spacing of the nearest point of the adjacent KeyPad is ≥0.2mm; the connection of KeyPad Pitch point 3) adjacent the closest point of spacing of KeyPad ≥0.2mm; surface wiring can not have the range covered by the dome, are taken via laser alignment manner. 4) The surface of the DOME pot can not be covered by the surface layer, and the laser through-hole method is adopted. There must be at least two exposed copper near the KeyPad for the DOME ground. At least two exposed copper should be used for the DOME ground. 5) There must be at least two exposed copper near the PCBKeyPad for DOME grounding. For reasons of small PCB size, it is impossible to make a complete and complete concentric circle. The KeyPad PCB is small in size. KeyPad, 6) If the PCB is too small, it is impossible to make a complete and complete concentric CirclePad. Aberdeen and KeyPad cooperation problem: reduce the size of the pot, so that after pressing, DOME pot and KeyPad cooperation issues need to consider the DOME pot and KeyPad cooperation problem: reduce the size of the pot, so that after pressing, the pot is straight Edge or opposite sides cannot exceed the KeyPad straight and shaped edges. The straight edge or the opposite side of the KeyPad straight edge and the alien edge cannot exceed the KeyPad straight edge and the alien edge. It can avoid the repeated rubbing of the solder mask on the PCB and cause the copper and the pot under the solder mask to be short-circuited, causing the KeyPad to fail. On the solder mask layer, the KeyPad fails the solder mask on the PCB, causing copper and pot under the solder mask to short-circuit, causing the KeyPad to fail. Shape positioning line (silk screen frame) shape positioning line (silk screen) device graphics, you must draw the component frame graphics, 1) When drawing BGA device graphics, you must draw component frame graphics, the purpose is to check the alignment . Right. For components related to structural cooperation such as battery sockets, cards, etc. 2) For components related to structural cooperation such as battery sockets, SIM cards, etc., when manufacturing PCB boards, the shape positioning frame of the components must be added, that is, the silk screen block diagram The board must be added with the shape positioning frame of the component, that is, the silk screen block diagram, and the gold wire can also be used as the shape positioning frame. Bit box. The chip structure member is preferably a component having a positioning hole. 3) The chip structure member is preferably a component having a positioning hole.