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The above guidelines shall apply to all PCB drawings.
1. The PCB Assembly Drawing – 16xxx
All sheets of all PCB Assembly drawings will carry the standard border, including the Title Block and Amendment Block (see Figure 1). Special notes related to standards, finishes and any other notable features which affect the PCB assembly shall be included in the first sheet. All notes should be collected in a single numbered list, except where individual notes may relate specifically to a particular view. In that case it is acceptable to place the unnumbered note close to the corresponding view.
The number of sheets in the drawing shall be kept to the minimum amount possible, by using larger page sizes where necessary. However, it is important that the drawing maintains clarity and avoids clutter; hence when necessary it is acceptable to increase the number of pages if this enhances readability. All sheets should have the same page size, where possible.
Where multiple variants of a PCB exist, each variant shall have as unique assembly number. All assemblies will refer to the same bare board number. The assemblies will traceable through their use of a common bare board.
Figure 1: The Standard PCB Assembly Border. Note that that Amendments block should be extended to the maximum amount of lines possible on the sheet, to allow room for detailed descriptions of modifications.
The circuit Schematic shall be included in the PCB assembly drawing. This shall include the following:-
i) The circuit diagram.
ii) The connector pin numbering and functions.
iii) Where a mechanical movement or contact system influences inputs or outputs of the circuit, such mechanical features should be represented in the schematic to aid understanding.
iv) Passive component values shall be shown on the schematic.
v) Semiconductor part numbers.
vi) All components will be identified by a designator that shall be referred to in the bill of materials and PCB assembly drawings. Refer to the table below for the prefixes to be used for each component type.
| Resistor | R |
| Capacitor | C |
| Diode | D |
| Transistor | Q |
| IC | U |
| LED | LED |
| Inductor | L |
| Connector | CON |
| Crystal | X |
| Switch | SW |
vii) Components shown on the schematic but not fitted must be identified by drawing a broken line box around the component. There should be text adjacent to the box “NOT FITTED”. Alternatively, the component may be crossed out on the schematic, and a note reading “CROSSED OUT COMPONENTS IN THE SCHEMATIC VIEW ARE NOT TO BE FITTED” shall be included. The best way to denote this shall be chosen according to the complexity of the schematic and the grouping of the components in question, in such a way as maintain clarity and avoid clutter in the schematic.
viii) Signals and terminal names required to improve understanding in other documents and software should also be shown in the schematic.
ix) For simplicity the schematic may be drawn in blocks with off page connectors.
x) The schematic may be spread over several sheets if necessary for clarity.
The Bill Of Materials (BOM) Table must identify all electronic components and their description in an unambiguous way. The component reference designators used in the BOM must be consistent with those shown in the Schematic View. All components shown in the schematic view have to be listed in the BOM. Those which are not to be mounted should be placed in separate lines and have an entry of ‘0’ in the ‘Quantity’ column (see Table 1).
The table shall have the following format: -
| BILL OF MATERIALS TABLE 1 | ||||||
| REF. DES. | QTY | DESCRIPTION | PACKAGE | PREFERRED SUPPLIER | ALT. SUPPLIER | PART NOS |
| R1 | RESISTOR 270Ω 1% - 0.25W | VISHAY | PHICOMP | CRCW-1206-270F-100-RT6 | ||
| R2 | NOT FITTED | N/A | N/A | N/A | ||
| C1,C2 | CERAMIC CAPACITOR 20%, 10nF, 50V | PANASONIC | VISHAY | ECJ1VB1H103M |
Table 1: Bill Of Materials Table
If PCB is to be assembled in-house at MEM, a new column with the MEM part number s MUST be added.
The preferred and alternative suppliers for the components, as well as the part number of the preferred supplier have to be listed in the BOM.
Microcontrollers should be identified and the software part number should be shown in the BOM as a component. Software numbers and revisions should be assigned according to the Software Development Procedure as follows: -
| 16xxx | - | Uxx | - | S | xx | |
| PCB article number | - | IC reference designator | - | Software Mark | Revision |
For example: 16234-U16-S02 refers to the software which should be in microcontrollers with reference designator U16 of PCB assembly 16234 and has revision 02.
The connector numbering shall be shown on the schematic view as described previously. The signals shall be described in a separate table that relates to the same connector pin numbering.
The table shall have the following format: -
| CONNECTOR PIN-OUT TABLE 2 | |
| PIN NUMBER | FUNCTION |
| +5V SUPPLY | |
| GROUND | |
| GEAR POSITION OUTPUT |
Table 2: Connector Pin-Out Table
An In-Circuit Testing table shall be included in the PCB assembly drawing. This table should indicate which electrical tests are to be performed on the PCBs after the components have been assembled. The table shall have the following format: -
| IN-CIRCUIT TESTING TABLE 3 | ||
| TEST | TESTING POINTS | EXPECTED VALUE |
| SW1 (NC) | TP2 – TP11 | <0.5 OHM |
| R1 // R2 | TP9 – TP12 | 470 OHMS ± 10% |
| D1 | TP2 – TP3 | 0.75 ± 0.05V @ I = 10mA |
Table 3: In-Circuit Testing Table
In the case that any programming and/or calibration procedure is required, this has to be specified in a separate process instructions document. The PCB assembly drawing shall contain a note (either in the general notes list or in this ICT table) referring to this process instructions document, including the file name and version.
In most cases, different resistors may be fitted on the PCB, depending on which of the specified LED illumination intensity bins are being assembled. In this case a table showing which resistor values are required for each LED intensity bin shall be included for each LED. It should be noted that two identical LEDs on the same PCB may require different resistor values for same bins, because the illumination may have different optical paths in the product.
When such resistor/LED bin tables are included, an additional table showing similar fields to those in the BOM table will be required for these resistors.
New Boards and or new Plastic will require LED tweaking across all acceptable BINs, resistors values for non-tweaked BINs shall be entered as TBE. This value will then be updated via a CN once the PCB assembler provides PCBs mounted with the available BINs.
A note in the 16xxx drawing is to require the PCB assembler to allow two weeks from the receipt of the new BIN PCBAs for a tweak and drawing update to occur.
The PCB assembly views should show the view of the PCB with the components placed on the board. Dimensioning is not necessary unless to define the location of a component with respect to some PCB datum. However it should be noted that SMD component locations are determined by the pad location and pad design and the tolerances will be wide, so if special tolerances are required, they should be indicated accordingly. Other dimensions shall be shown as REF DIMS.
The PCB assembly views normally occupy the last sheet of the drawing.
Where applicable, views showing connector dimensions, materials, plating and coining details shall be included in the PCB assembly drawing.
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| DWG NO. (Drawing Number) | | | The Bare Board Drawing - 44xxx |