DFM (Design for manufacturability) is a manufacturing-oriented design, which is the core technology of concurrent engineering. Design and manufacture is the most important part of the product life cycle, parallel engineering is to start in the design of the product should consider the manufacturability and assembly and other factors. So DFM is the most important support tool in parallel engineering. Its key is the design of information technology analysis, manufacturing rationality evaluation and improvement of the design recommendations. In this paper, we will be on the PCB process in the DFM general technical requirements to do a brief introduction.
First, the general requirements
1, the standard PCB design as a general requirement, standardize the PCB design and manufacturing, to achieve effective communication between CAD and CAM.
2, I Division in the document processing priority to design drawings and documents as a basis for production.
Second, PCB material
1, substrate
PCB substrate is generally made of epoxy glass cloth over copper, that FR4. (Including single panel)
2, copper foil
A) more than 99.9% of electrolytic copper;
B) double-layer finished product surface copper foil thickness ≥ 35? M (1OZ); have special requirements, specified in the drawings or documents.
Third, PCB structure, size and tolerances
1, structure
A) The relevant design elements that make up the PCB should be described in the design drawings. The appearance should be unified with Mechanical 1 layer (priority) or Keep out layer. If used in the design file at the same time, the general keep out layer used to shield, do not open, and mechanical 1 said forming.
B) in the design drawings that open long SLOT hole or hollow, with Mechanical 1 layer to draw the corresponding shape can be.
2, thickness tolerance
3, the size of the tolerance
PCB dimensions should conform to the design drawings. When the pattern is not specified, the dimensional tolerance is ± 0.2mm. (Except V-CUT products)
4, flatness (warpage) tolerance
The flatness of the PCB should conform to the design pattern. When the pattern is not specified, follow the following
Fourth, printed wire and pad
1, layout
A) Printed wire and pad layout, line width and line distance in principle according to the design pattern. But I will have the following Secretary: the appropriate process according to the requirements of the line width, PAD ring width to compensate, single panel general I will try to increase the PAD, to enhance the reliability of customer welding.
B) When the design line spacing can not meet the requirements of the process (too close may affect the performance, manufacturability), Division I according to the pre-design specifications appropriate adjustments.
C) In principle, we recommend that when the customer designs a single and double panel, the diameter of the through hole (VIA) is set to 0.3mm or more, the outer diameter is set to 0.7mm or more, the line spacing is 8mil, and the line width is designed to be 8mil or more. To minimize the production cycle, reduce manufacturing difficulty.
D) Our minimum drilling tool is 0.3, the finished hole is about 0.15mm. The minimum line spacing is 6 mil. The thinest line width is 6 mil. (But the manufacturing cycle is longer, the cost is higher)
2, wire width tolerance
Printed wire width tolerance Internal control standard is ± 15%
3, the grid processing
A) In order to avoid the wave soldering copper surface after the bubble and heat due to thermal stress PCB board bending, copper on the proposed laying into a grid form.
B) its grid spacing ≥ 10mil (not less than 8mil), grid line width ≥ 10mil (not less than 8mil).
4, the thermal pad (Thermal pad) processing
In a large area of ​​the ground (electricity), often the components of the legs connected to the connection legs to deal with both the electrical performance and process needs, made of cross-pad (insulation plate), can be welded in the cross-section Excessive heat dissipation and the possibility of generating solder joints is greatly reduced.
5, aperture (HOLE)
1, metallization (PHT) and non-metallization (NPTH)
A) Our company defaults to the following ways for non-metallized holes:
When the customer in the Protel99se Advanced Properties (Advanced menu will be removed hook items) to set the hole non-metallization properties, I am the default non-metallized hole.
When the customer in the design file directly with the keep out layer or mechanical 1 layer arc that punch (no further hole), our company default to non-metal hole.
When the customer placed near the hole NPTH words, our company default for this hole non-metallic.
When the customer in the design notice clearly requires the corresponding aperture non-metallic (NPTH), according to customer requirements.
B) In addition to the above components hole, mounting holes, vias, etc. should be metallized.
2, aperture size and tolerance
A) Design the PCB element hole in the pattern, the mounting hole defaults to the final finished aperture size. Its aperture tolerance is generally ± 3mil (0.08mm);
B) vias (ie VIA holes) Our general control is: Negative tolerances are not required, the positive tolerance is controlled within + 3mil (0.08mm).
3, thickness
The average thickness of the copper layer of the metallized hole is generally not less than 20 μm and the thinnest is not less than 18 μm.
4, hole wall roughness
PTH hole wall roughness is generally controlled at ≤ 32um
5, PIN hole problem
A) Our CNC milling machine positioning needle minimum 0.9mm, and positioning of the three PIN holes should be triangular.
B) When the customer has no special requirements, the design file in the aperture are <0.9mm, I will be in the board of blank lines or large copper on the appropriate location plus PIN hole.
6, SLOT hole (slot) design
A) Suggest SLOT hole with Mechanical 1 layer (Keep out layer) to draw the shape can be; can also be used to show the hole, but the hole should be the same size, and the hole in the same horizontal line.
B) Our smallest slot knife is 0.65mm.
C) When the SLOT hole is used to shield, to avoid high and low voltage between the creepage, it is recommended that the diameter of 1.2mm or more to facilitate processing.
        Six, solder mask layer
1, coating parts and defects
A) In addition to pads, MARK points, test points, etc. outside the PCB surface, should be coated with solder mask layer.
B) If the customer is represented by FILL or TRACK, the corresponding size graphic must be drawn at the Solder mask layer to indicate the tin on it. (I strongly recommend that the design before the non-PAD form that disk)
C) If you need to heat on a large copper or spray on the line, you must also use the solder mask layer (Solder mask) layer to draw the corresponding size of the graphics to indicate the place on the tin.
2, adhesion
The adhesion of the solder resist layer is in accordance with the requirements of US IPC-A-600F Level 2.
3, thickness
The thickness of the solder mask is in the following table:
Seven, character and etch mark
1, the basic requirements
A) PCB characters should generally be word high 30mil, word width 5mil, character spacing 4mil above design, so as not to affect the text of the discernable.
B) Etch (metal) characters should not bridge with the wires and ensure adequate electrical clearance. General design by word height 30mil, word width 7mil above design.
C) customer character no clear requirements, our company will generally be based on our company's process requirements, the proportion of the characters with the appropriate adjustments.
D) When the customer is not clearly defined, I will be in the Secretary for silk screen in the appropriate location according to our process requirements printed with our trademark, number and cycle.
2, the text on the PAD \ SMT processing
Tray (PAD) can not have silk screen layer logo to avoid Weld. When the customer has the design PAD \ SMT, I will be appropriate for mobile processing, the principle is not to affect its identity and device correspondence.
The concept of the layer and the design of the processing point of the MARK point
1, double-panel Division I default to the top (that is, Top layer) for the positive view, topoverlay silk screen layer character is positive.
2, single-panel to the top layer (Top layer) draw line layer (Signal layer), then the layer line for the positive side.
3, single-panel to the bottom (Top layer) draw line layer (Signal layer), then the layer line for the perspective.
The design of the MARK point
4, when the customer for the puzzle file with a surface patch (SMT) need to Mark point positioning, to put the MARK, for the circular diameter of 1.0mm.
5, when the customer has no special requirements, I Division in the Solder 1.5mm arc to indicate the non-stop solder to enhance the recognition. Place the FMask layer one
6, when the customer for the puzzle file has a surface patch process has not put MARK, the Division I generally in the process side of the diagonal position of the middle plus a MARK point; when the customer for the puzzle file surface patch no process edge , Generally need to communicate with customers need to add MARK.
Nine, on the V-CUT (cut V-slot)
1, V cut the plywood board and the board does not leave the gap, but pay attention to the conductor and V cut the center line distance. Under normal circumstances V-CUT line on both sides of the conductor spacing should be more than 0.5mm, that is a single plate in the conductor from the board edge should be more than 0.25mm.
2, V-CUT line representation: the general shape for the keep out layer (Mech 1) layer, then the board to be V cut the place only need to use the keep out layer (Mech 1) layer and the best in the board The connection indicates V-CUT.
3, as shown below, the general V after the residual depth of 1/3 thickness, and the other according to the customer's residual requirements may be appropriate to adjust.
4, V cut the product after breaking the glass fiber yarn has been loose phenomenon, the size will be slightly worse, individual products will be larger than 0.5mm.
5, V-CUT knife can only go straight, can not take the curve and polyline; and can pull the board thickness is generally above 0.8mm.
10, surface treatment process
When the customer has no special requirements, our surface treatment by default the use of hot air leveling (HAL) way. (Ie spray tin: 63 tin / 37 lead)
Above DFM general technical requirements (single and double panel part) for our customers in the design of PCB documents when the reference, and hope to reach some of the above aspects of consistency, in order to better achieve CAD and CAM communication, Manufacturing design (DFM) common goal, to better shorten the product manufacturing cycle, reduce production costs.
Eleven, concluding remarks
The above DFM general technical requirements (single and double panel part) only for the century core for customers in the design of PCB documents to provide a reference, and hope to reconcile the above aspects of coordination to better achieve CAD and CAM communication, better (DFM) to achieve common goals, shorten the product manufacturing cycle, reduce production costs.