Overview of technical requirements for PCB process DFM

- Sep 22, 2018-

DFM (Design for manufacturability) is the core technology of concurrent engineering.Design and manufacture are the two most important links in the product life cycle. Parallel engineering is to consider factors such as manufacturability and assembling ability of the product when designing.So DFM is the most important support tool in parallel engineering.The key point is the technological analysis of design information, the evaluation of manufacturing rationality and the suggestion of improving design.In this paper, we briefly introduce the general technical requirements of DFM in PCB process.

1. General requirements

1. This standard is the general requirement of PCB design, standardizes PCB design and manufacturing, and realizes the effective communication between CAD and CAM.

2. Our company shall give priority to design drawings and documents as the production basis when processing documents.

2. PCB materials

1, base material

The base material of PCB is usually epoxy glass coated copper plate, namely FR4.(including single panel)

2, copper foil,

A) more than 99.9% electrolytic copper;

B) the thickness of copper foil on the finished surface of double-layer plate is greater than or equal to 35?M (1OZ);Special requirements shall be specified in the drawing or document.

3. PCB structure, size and tolerance

1, structure,

A) the relevant design elements constituting the PCB shall be described in the design drawing.The appearance should be expressed by Mechanical 1 layer (priority) or Keep out layer.If used in the design file at the same time, generally keep out layer is used to shield, not to open holes, and is formed by mechanical 1.

B) represent long SLOT holes or hollow out in the design drawing, and draw the corresponding shapes using Mechanical 1 layer.

2. Plate thickness tolerance

3. Dimensional tolerance

PCB dimensions shall be in accordance with the design requirements.The dimensional tolerance is + / - 0.2mm when the pattern is not specified.(except v-cut products)

4. Flatness (warping) tolerance

The flatness of the PCB shall conform to the design pattern.When the pattern is not specified, it shall be executed as follows

Printing wires and welding pads

1, the layout

A) the layout, wire width and wire spacing of the printed wires and pads shall, in principle, be in accordance with the design pattern.However, our company will make the following treatment: compensate the wire width and PAD ring width according to the process requirements; generally, our company will increase the PAD as much as possible on a single panel to enhance the reliability of customer welding.

B) when the design line spacing fails to meet the process requirements (too dense may affect the performance and manufacturability), our company shall adjust the design according to the pre-production design specifications.

C) in principle, our company suggests that when designing single and double panels, the internal diameter of VIA should be set above 0.3mm, the external diameter should be set above 0.7mm, the line spacing design should be 8mil, and the line width should be set above 8mil.Minimize production cycle and manufacturing difficulty.

D) our minimum drill cutter is 0.3, and its finished hole is about 0.15mm.The minimum spacing is 6mil.The smallest line width is 6mil.(but the manufacturing cycle is longer and the cost is higher)

2. Wire width tolerance

The internal control standard of width tolerance of printed conductor is + / - 15%

3. Grid processing

A) in order to avoid frothing of copper surface and bending of PCB plate due to thermal stress after heating during wave peak welding, it is recommended to lay the large copper surface in grid form.

B) grid spacing is greater than or equal to 10mil(not less than 8mil) and grid line width is greater than or equal to 10mil(not less than 8mil).

4. Treatment of Thermal pad

In the large area of grounding (electricity), the legs of the components are often connected with them, and the processing of the connecting legs gives consideration to the electrical properties and technological requirements, and the cross welding panel (heat insulation panel) is made, which can greatly reduce the possibility of virtual welding spot due to excessive heat dissipation of the section during welding.

V. aperture (HOLE)

1. Definition of PHT and NPTH

A) our company defaults to non-metallic hole as follows:

When the customer sets the non-metallization property of mounting holes in the Advanced properties of Protel99se (removal of the plated item in the Advanced menu), our company defaults to non-metallization holes.

When the customer directly USES the "keep out layer" or "mechanical 1 layer arc" in the design file to indicate punching (no more separate holes), our company defaults to non-metallic holes.

When the customer places the word NPTH near the hole, our company defaults to non-metallization for the hole.

When the customer clearly requests the corresponding hole size non-metallization (NPTH) in the design notice, the process shall be handled according to the customer's requirements.

B) the element holes, mounting holes and conducting holes shall be metallized except the above.

2. Aperture size and tolerance

A) the PCB element holes and mounting holes in the design drawing default to the final product aperture size.The aperture tolerance is generally + / - 3mil (0.08mm).

B) VIA hole (i.e., VIA hole) is generally controlled as follows: negative tolerance is not required, and positive tolerance is controlled within + 3mil (0.08mm).

3, the thickness of the

The average thickness of the copper coating of the metallized hole is generally not less than 20?M, the thinnest part is no less than 18, right?M.

4. Hole roughness

PTH hole wall roughness is generally controlled at no more than 32um

5. PIN hole problem

A) the minimum positioning PIN of our CNC milling machine is 0.9mm, and the three PIN holes to be positioned should be triangular.

B) when the customer has no special requirements and the holes in the design documents are all < 0.9mm, our company will add PIN holes to the blank line or the appropriate location on the large copper surface.

6. Design of SLOT holes (SLOT holes)

A) it is suggested that SLOT holes use Mechanical 1 layer (Keep out layer) to draw its shape;It can also be represented by a connecting hole, but the connecting hole should be of the same size and the center of the hole is on the same horizontal line.

B) our smallest groove cutter is 0.65mm.

C) when the SLOT hole is used for shielding to avoid power creep between high and low voltage, it is recommended that its diameter is above 1.2mm to facilitate processing.

Vi. Resistance welding layer

1. Coating site and defects

A) the resistance welding layer shall be applied on all PCB surfaces except the pad, MARK point, test point, etc.

B) if the customer USES the disk represented by FILL or TRACK, a graph of the corresponding size must be drawn on the Solder mask layer to indicate the Solder coating.(we strongly suggest not using non-pad format before design)

C) if it is necessary to dissipate heat on the large copper sheet or spray tin on the lines, the Solder mask layer shall be used to draw a figure of the corresponding size to represent the tin on the place.

2. Adhesion

The adhesion of the resistance welding layer is required by grade 2 of American ipc-a-600f.

3, the thickness of the

The thickness of the resistance welding layer conforms to the following table:

Characters and etching marks

1. Basic requirements

A) the characters of PCB should generally be designed with the character height of 30mil, the word width of 5mil and the character spacing of 4mil, so as not to affect the discriminability of the text.

B) the etching (metal) character shall not be bridged with the wire and sufficient electrical clearance shall be ensured.The general design by the word height 30mil, the word width 7mil above the design.

C) when there is no specific requirement for the customer's characters, our company will generally adjust the matching proportion of the characters according to our technical requirements.

D) when the customer has no specific requirements, our company will print our company's trademark, material number and cycle in the appropriate position of the screen printing layer in the board according to our company's technical requirements.

2. Processing of PAD\SMT on text

There should be no screen mark on the PAD to avoid virtual welding.When the customer has designed the PAD\SMT, our company will do the appropriate mobile processing, the principle is not to affect its identification and device compatibility.

Viii. Concept of layer and design of processing layer of MARK point

1. By default, the Top layer is used as the facing surface and the topoverlays are positive.

2. The single panel USES the Top layer to draw the Signal layer, which indicates that the layer line is the facing surface.

3. The single panel USES the Top layer to draw the Signal layer, which indicates that the layer is perspective.

MARK point design

4. When the customer needs to use Mark point to locate the surface patch (SMT) for the assembly file, Mark shall be put, which is circular with diameter of 1.0mm.

5. When the customer has no special requirements, our company USES the 1.5mm arc of Solder to represent the Solder barrier flux, so as to enhance the identification.Place a FMask layer

6. When the customer does not put MARK on the surface patch or process edge of the assembly file, we usually add MARK point in the diagonal center position of the process edge.When the customer has a surface patch without a process edge for the jigsaw file, it is generally necessary to communicate with the customer to add MARK.

9. About v-cut (CUT V groove)

1. No gap is left between v-cut panels and plates, but pay attention to the distance between conductor and v-cut center line.Generally, the conductor spacing between the two sides of the v-cut line should be above 0.5mm, which means that the conductor spacing between the side of the single plate should be above 0.25mm.

2. The expression method of v-cut line is as follows: generally, the contour is represented by the keep out layer(Mech 1) layer. Then, only use the keep out layer(Mech 1) layer to draw the area where V should be CUT in the board, and it is better to mark the v-cut type at the board connection.

3. As shown in the following figure, the residual depth of v-cut is 1/3 of the plate thickness, which can be adjusted appropriately according to the customer's residual thickness.

4. After the product break, V will be pulled apart due to the phenomenon of glass filament. The size will be slightly out of tolerance, and some products will be larger than 0.5mm.

V-CUT knife can only go straight line, not curve and broken line;Generally, the thickness of the drawable wire plate is above 0.8mm.

Surface treatment process

When the customer has no special requirements, our surface treatment is by default in the way of hot air leveling (HAL).(i.e. tin spray: 63 tin /37 lead)

Above DFM general technical requirements (single and double pane) for our customers in the design of PCB file reference, and hope to be able to reach a certain agreement on the above, in order to better realize the CAD and CAM communication, better realize the manufacturability design (DFM), the goal of better shorten the product manufacturing cycle, reduce the production cost.

conclusion

Above DFM general technical requirements (single and double panel part) is the core for the customer provide reference when designing PCB file, and hope to be able to just above aspects mutually agreed to reconcile, to better the implementation of the CAD and CAM communication, better realize the manufacturability design (DFM) common goals, shorten the product manufacturing cycle, reduce the production cost.