What should be paid attention to when PCB proofing?

1. Outer circuit design rules:

(1) Welding ring (Ring ring): The welding ring of the PTH (copper-plated hole) hole must be 8mil larger than the single side of the drilled hole, that is, the diameter must be 16mil larger than the drilled hole. The welded ring of the Via hole must be larger than the drilled single side 8 mils larger, the diameter must be 16 mils larger than the drilled hole. In short, whether it is a through hole PAD or Via, the inner diameter must be greater than 12 mils, and the outer diameter must be greater than 28 mils. This is very important!

(2) The line width and line spacing must be greater than or equal to 4 mils, and the distance between holes should not be less than 8 mils.

(3) The etching word line width of the outer layer is greater than or equal to 10mil. Pay attention to the etching word instead of silk screen.

(4) The circuit layer is designed with a grid board (copper is paved into a grid), and the rectangle of the grid space is greater than or equal to 10*10mil, that is, the line spacing should not be less than 10mil when the copper is laid.

The grid line width is greater than or equal to 8mil. When laying a large area of copper, many materials suggest that it be set into a mesh.

However, some engineers believe that in terms of heat dissipation, the advantages of copper grids cannot be generalized. If local heating may cause PCB deformation, grid layouts should be used on the condition of loss of heat dissipation and preservation of the integrity of the PCB. copper.

The advantage of this kind of copper paving relative to paving copper is that although the surface temperature of the board is increased to a certain extent, it is still within the range of commercial or industrial standards, and the damage to the components is limited.

However, if the direct consequence of PCB board bending is the appearance of virtual solder joints, it may directly lead to line failure. The comparative result is that less damage is better, and the real heat dissipation effect should still be solid copper.

In practical applications, the copper in the middle layer is basically seldom grid-like, that is, the uneven stress caused by temperature is not as obvious as the surface layer, and solid copper with better heat dissipation effect is basically used.

(5) The distance between the NPTH hole and the copper is greater than or equal to 20 mils.

(6) For the board formed by the gong board (milling cutter), the distance between the copper and the forming line is greater than or equal to 16 mils, so in the layout, the distance between the trace and the frame should not be less than 16 mils. In the same way, when slotting, the distance to copper must be greater than or equal to 16 mils.

(7) For die-punched boards, the distance between the copper and the molding line is greater than or equal to 20 mils. If the board you draw may be mass-produced in the future, in order to save costs, you may need to open the mold, so you must foresee it when designing.

  • V-CUT (usually draw a line on the Bottom Mask and Top Mask layers, it is best to mark the place where V-CUT is required) The formed board should be designed according to the thickness of the board;

[1] The board thickness is 1.6mm, and the distance between the copper and the V-CUT line is greater than or equal to 0.8mm (32mil);

[2] The thickness of the board is 1.2mm, and the distance between the copper and the V-CUT line is greater than or equal to 0.7mm (28mil);

[3] The thickness of the board is 0.8mm-1.0mm, and the distance between the copper and the V-CUT line is greater than or equal to 0.6mm (24mil);

[4] The board thickness is less than 0.8mm, and the distance between the copper and the V-CUT line is greater than or equal to 0.5mm (mil);

[5] For the golden hand board, the distance between the copper and the V-CUT line is greater than or equal to 1.2mm (mil).

Note: Don’t set such a small spacing when jigsaw puzzles, try to be as large as possible.

2. Design rules of inner circuit:

  • Welding ring (Ring ring): The welding ring of the PTH hole must be 8mil larger than the single side of the drilled hole, that is, the diameter must be 16mil larger than the drilled hole. The welding ring of the Via hole must be 8mil larger than the single side of the drilled hole, and the diameter must be 16mil larger than the drill hole.
  •  The line width and line spacing must be greater than or equal to 4mil.

(3) The etching word line width of the inner layer is greater than or equal to 10 mils.

(4) The distance between the NPTH hole and the copper is greater than or equal to 20 mils.

(5) For the board formed by the gong board (milling cutter), the distance between the copper and the forming line is greater than or equal to 30 mils (generally 40 mils).

(6) The distance from the PTH hole of the inner layer without solder ring to the copper foil is maintained at least 10mil (four-layer board), and at least 11mil for the six-layer board.

(7) When the line width is less than or equal to 6mil lines and there is a hole in the pad, a teardrop must be added between the line and the pad.

(8) The isolation area between the two large copper surfaces is more than 12mil.

  • Heat dissipation PAD (plum pad), the distance from the edge of the hole to the inner circle is greater than or equal to 8mil (ie Ring ring), the distance from the inner circle to the outer circle is greater than or equal to 8mil, and the opening width is greater than or equal to 8mil. Generally there are four openings , At least two openings must be ensured.

3. Drilling design rules

(1) In principle, the PCB board factory designs the “8”-shaped hole into a slot (annular hole). Therefore, it is recommended to make it into a ring shape as much as possible in the layout. It does not have this function. You can put more than N circles and stack them as much as possible.

In this way, there will be no “dogs wanting teeth” in the ring groove at the end, and the plate factory will not break the drill bit because of your slot!

(2) The minimum mechanical drilling hole diameter is 0.25mm (10mil), and the general hole diameter design is greater than or equal to 0.3mm (12mil).

If it is smaller than this or just 0.25mm, the board factory will definitely find you. why,? [You can find the answer you want in (5)]

(3) The minimum slot aperture is 0.25mm (10mil), and the general aperture design is greater than or equal to 0.3mm (12mil). 【Same as (2)】

(4) As a general practice, only the mechanical drilling unit is mm; the other units are mil. My drawing habit is, except for the library because I need to measure the size in mm, the others all use mil as the unit. The mil unit is small, which is really convenient.

(5) The aperture of laser drilling (laser) is generally 4mil (0.1mm)-8mil (0.2mm). Generally, boards with more than 6 layers and very dense will use this technology.

For example, mobile phone motherboards, of course, the price will definitely increase by an N level.

4. Principles of text design:

The line width of the text is more than 6mil, the height of the text is more than 32mil, and the line width of the text frame is more than 6mil.

5. Design principles of hole copper and surface copper

(1) General finished surface copper 1OZ (35um) board, hole copper 0.7mil (18um).

(2) General finished copper 2OZ (70um) board, hole copper 0.7mil (18um)-1.4mil (35um).

6. Principles of solder mask design

(1) The solder mask is 3mil (clearance) larger than the pad. [Many software is set by default, you can look for it yourself! 】

(2) The solder-proof distance line (copper) is greater than or equal to 3mil.

(3) Green oil bridge ≥ 4mil, that is, the gap (dam) between the solder masks of the IC pins.

(4) The opening and cover line of the BGA position is greater than or equal to 2mil, and the green oil bridge is designed.

(5) The gold finger part of the gold finger board must be solder-proof and open, including fake fingers.

(6) The wire diameter of the solder mask type is ≥8mi, and the character height is ≥32mil.