Connecting surfaces according to IPC-7531

Transcription

1 Chapter 1 Connecting surfaces according to IPC-7531 For connection surfaces, 3 sealing stages and corresponding sizes are selected Are defined. Example: RESC2012X06M / N / L Step A: Maximum (Most) overlap of the pad (M as the last character in the parts-designation) Level B: Mean (Nominal) overlap of the land (N as the last character in the components designation) Step C: Min (Least) overlap of the pad (L as the last character in the components designation)

2 Step A M (must): Maximum (largest) projection of the connection surface In the development, applications were taken into account which had a low structural weight, with a view to as good as possible Suitability for hand and wave soldering of chip components, as well as with gullwing connectors. The connection geometry, which is also used for component families with inwardly bent or J-shaped terminals can also be used for reflow soldering. Step B N (nominal): Middle (normal) projection of the connection surface With an average structural weight, assembly in reflow soldering processes and provides adequate process conditions for manual or wave soldering. Step C L (Least): Minimum (minimum) projection of the connection surface Products with high constructional properties such as portable and mobile devices, require contact surfaces with the slightest overhang. These are suitable may not apply to all categories of use. Although the density steps are not identical to the producibility stages, the use of the performance classes (1, 2, 3) is connected with the density steps (A, B, C) nevertheless a reference to the design requirements of an electronic module.

3 1.1 Structure The protrusion of the connection surfaces depends on different sides in different areas. The joint is considered a foot, with toes, heel and sides. Correspondingly, the designated areas with JT, JH and JS. For these areas sizes were determined which correspond to the dimensions of the connection or pins. This results in the size of the pad (pad). The following is a list of some basic values. For more precise values and the exact derivation of the calculation I would like to the original documentation. The Courtyard value specifies the outer distance to the connection area again. It is rounded up to 0.05 mm each. Exception: Chip components 0.02mm Typical values (mm): Level Area A (M) B (N) C (L) JT JH JS Courtyard For smaller components, the heel value is halved. Is the area under the housing, it decreases in turn, or even can negative. For chip components, it is set to 0. Molded (embedded) components are the exception. The side value decreases with small pin pitches (pitch) or can also become negative. For chip components it is {0.05, 0, -0.05} mm.

4 1.1.1 Distance between the connection surfaces The distances between the pads are determined either by the pin spacing of the component, or by their outer dimensions. The condition of the minimum clearance of the circuit board manufacturer must, of course, be adhered to. The component manufacturers generally specify tolerances to the component masses. This relates to the external dimensions, the dimensions of the housing, as well as the dimensions of the connections. Further tolerances are defined by the circuit board manufacturer as the tolerance value of the contour and by the module manufacturer as the position tolerance of the placed components. The pad size is calculated in addition to the range values of the connection taking into account the tolerance of the connections, the contour tolerance and the position tolerance. For the determination of the pad distance over the housing, the tolerance of the total mass, the tolerance and the load tolerance are required. For the determination of the courtesy, the tolerance of the contours and the positional tolerance are also added. The tolerance values are calculated from a mixing value of the effective maximum tolerance (worst case) and an RMS value. The formula for this can be found in the IPC-7351B.

5 A completed footprint to the above IC: The red pads correspond to the copper layer, the shaded extension the retraction of the solder mask. Yellow corresponds to the mounting pressure. The green rectangle characterizes the Courtyard, the cross in the center the origin. The height of the components is immaterial. Exception: aluminum capacitors in a cylindrical vertical design. At this point, it should be noted that components placed directly next to one another can lead to soldering problems with high heights or differences in heights. In general, a greater distance from the courtyard is to be taken into account in such parts. In case of doubt, the sub-contractor should be consulted. In the case of connections which are arranged square or rectangular, the calculation is expanded accordingly to the additional axes and ground. In the case of housings without connecting pins (QFN, LCC etc.), on the other hand, the total mass falls away and only the housing mass is important. At most, a pullback of the connections from the housing edge is added.

6 Some terms English Body Width Body Length Lead Span Width Lead Span Length Pitch Pullback Total Height Standoff Lead Length Lead Width Exposed Pad Leaded Leadless German Breite Gehäuse Länge Gehäuse Breite gesamt Länge gesamt Abstand Rückzug Höhe gesamt Höhe über Leiterplatte Länge Pin Breite Pin Thermal Pad Mit Anschluss-Pins ohne Anschluss-Pins

7 1.1.2 Identification Pin 1 is always marked when a distinction is necessary. The marking should still be visible after placement. Marking is carried out with SMD components through a circular point near the pad. For ICs, 1 corner of the housing's figure is beveled on placement pressure and placement plans if a chamfer is actually used as location marking. On pin assignments, pin 1 indicates a circular point within the housing image. For SO and DIL housings it is usual to draw a semicircular indentation on the side of pin 1. Many ICs are actually characterized in this way. This is partly indicated by a triangle. In the case of THT components, pin 1 is marked on the mounting pressure by a surrounding rectangle or a circle. If the space is sufficient, a circular point is placed near the pad. For a better distinction, pin 1 is designed as a rectangular pad, while all others are round or oval. For simple unpolarized components, no marking is necessary Polarized components Pin 1 is always the "positive" pin. The type of marking of polarized components can be included in the footprint. It is particularly useful for placement and orientation.

8 1.2 Zero position according to IEC The standard IEC specifies: Components and footprints are drawn from the top. The origin point is marked with '+' or 'x'. The origin of the footprint can be from the point of origin for the placement be different. A rectangle surrounding a component contour and footprint with a view of above guarantees a minimum for electrical and physical distance as courtyard. The origin point described above should be assigned to the component and the footprint. The arrangement of footprints is unified by the classification and form of the footprints components according to IEC to IEC The information of the footprints is dependent on the angle of the component support systems (tape, tray, tube etc.) independently. Pin 1 in the Footprint is to be used with any polarization mark on the component. The orientation of the component should be left to the left of the component position. Components, footprints and courtyards are supposed to be in the computer library are the same and use the same origin coordinates. It is recommended to design the origin as the component is placed on the finished printed circuit board, typically centered within of the component. Only the rotation of the components with more than 2 pins should to change the rules for rendering to Level A or B to fulfill. Level A Rule: Pin 1 should be used for the display of components with more than 2 connections left, as described in the basic rule. However, pin 1 should be on the upper or upper left. Own note: Well, if that is not a contradiction... Level B Rule: Pin 1 should be used for the display of components with more than 2 connections left, as described in the basic rule. However, pin 1 should be on the left or left at the bottom.