The wiring diagram behind the physical PCB and the factory drawings are two different things. PCB factory drawings describe the physical and electrical attributes in the circuit diagram of “Gerber data file”. The two documents complement each other.
Memo needs to define options and exceptions.
Although there are some specifications that drive the PCB design process, in these specifications, the options are almost unlimited. Everything has rules, but almost all rules have exceptions. Defining these options and exceptions to the rules is a task of the memorandum.
Explanatory memorandum: unless otherwise specified.
“Unless otherwise specified” is a vague term that allows rules to achieve hierarchical cascade. Legal documents and contract documents are the highest arbiters of PCB manufacturing process, followed by supporting purchase orders, and then the specific design instructions of pyramid structure. The design notes here include manufacturing drawings and assembly drawings, so I won’t repeat them here.
IPC-6012 defines the general precautions for manufacturing rigid plates, IPC-6013 is for flexible printed circuit board, and IPC-600 is a comprehensive document involving all processes. By referring to each other, there are dozens of standards applicable to PCB manufacturers-unless otherwise specified. Therefore, the purpose of creating the explanatory memorandum is to increase the design for manufacturability (DFM) without violating local laws, contracts and purchase orders.
1, follow the standard:
A. make PCB according to the current revision of IPC-6012 level 2.
B. Explain dimensions and tolerances according to the current revision of ASME Y14.5M
C. Don’t enlarge the drawing.
2. Materials:
A. FR4 Tg 180 C or equivalent.
B. The equivalent materials shall meet RoHS standards, be halogen-free and approved by your company.
C. The thickness of a single copper foil should be within the interval defined by stacking. See details a
3. Flatness:
A. the bow and warpage of the assembled sub-board or single board shall not exceed 0.025 mm/mm
B. Test according to Section 2.4.22 of the current version of IPC-TM-650.
4. Etching geometry:
A. Measure the width on the basis of metallization.
B. Minimum line width: 0.nn mm for outer layer and 0.nn mm for inner layer.
C. The final line width and terminal area will not deviate from the 1: 1 main pattern image by +/- 0.025 mm or 20%, and the comparison benchmark will take the minimum value of the above two.
5. Surface treatment: (Select the appropriate surface treatment (ES))
A. Electroless nickel-palladium-gold plating is carried out according to the current revision of IPC4556. The exposed metal can be 118-236 microinches of chemical nickel, 2-6 microinches of chemical palladium, and 1.2 microinches of gold.
B. Electroless gold plating according to the current revised version of IPC-4552. 118-236 micron inches of chemical nickel and 2-5 micron inches of gold can be selected for the exposed metal.
6. Destructive testing:
A. Some samples and reports should be provided to the design and engineering department of your company.
B. Each shipment needs to include solder samples used in the lead-free soldering process.
C. X-OUT panel can be used for welding samples.
7. Via:
A. The plating material in the hole should be continuous electrolytic copper with a minimum thickness of 0.025mm
B. Minimum hole size: 0.nn mm.
C. Measure the hole size after electroplating.
D. Check the drilling chart to determine the hole size and tolerance.
E. the positions of all holes should be within 0.08 mm of the true position provided by CAD data.
8. Solder resist layer:
A. according to the material specified in TYPE B of the current version of IPC-SM-840, realize solder resist (SMOBC) on the bare copper of the primary and secondary surfaces.
B. color: dumb green
C. The thickness of liquid photo-induced (LPI) solder resist is between 0.001mm and 0.002mm, and it is halogen-free.
D. No leakage is allowed on the exposed SMD pad.
E. there are no exposed wires.
9. Screen printing layer:
A. White epoxy resin and non-conductive non-nutritional ink are used for the screen printing layers of the main surface and the secondary surface.
B. Any unspecified screen printing width should be 0.13mm.
C. Ensure that the silk screen layer does not touch any exposed metal.
D. Supplier date code, LOGO, unordered list and any additional marks are located on the secondary side.
10. Remove any burrs and sharp edges with radius greater than 0.003mm
11. Non-destructive evaluation:
Answer: All printed circuit boards (PWBS) must pass 100% of the electrical tests defined by IPC-356 NETLIST to meet the level 2 requirements in the revised version of IPC-9252.
B. Certificate of conformity should be provided with each shipment.
12. Scrap board:
A. Scrap boards that do not meet all specifications are marked with permanent marks on both sides of PCB.
B. Products without any scrap boards will be packaged together.
C. Products with n or fewer scrap boards should be packaged separately from products without scrap boards.
D. Products with more than N scrap boards should not be packaged.
13.PCB packaging requirements:
A.PWBS shall be packed in an inner container sealed in vacuum.
B. The outer container should be sufficient to prevent damage during transportation and handling.
14. Impedance (the tolerance of all impedances is within plus or minus ten percent)
A. The impedance of all wires with 0.nn mm line width on the outer layer should be 50 ohms.
B. The differential impedance of all 0.nn mm wide /0.nn mm spaced wire pairs on the outer layer should be 90 ohms.
C. The differential impedance of all 0.nn mm wide /0.nn mm spaced wire pairs on the inner layer should be 90 ohms.
D. The supplier can adjust the design geometry up to+/-20% to achieve the target impedance. The line width, spacing or dielectric thickness adjustment of more than 20% needs the approval of your engineering department.
