What is PCB stackup design

1、4 layer pcb stackup：TOP-SIG－GND－BOT

2、6 layer pcb stackup

3、8 layer pcb stackup

4、10 layer pcb stackup

5、12 layer pcb stackup

PP (Prepreg) : laminated as a semi-cured sheet, also known as prepreg material, impregnated with resin and cured to an intermediate degree (B stage) sheet material. It is mainly used for bonding materials and insulating materials of conductive graphics in the inner layer of multi-layer printed boards. After the Prepreg is laminated, the semi-cured epoxy is extruded and begins to flow and solidify, bonding the multilayer circuit board together and forming a reliable insulator. In simple terms, the PCB industry prepreg semi-cured sheet is equivalent to the role of glue, with prepreg a few core lamination (lamination) method to form a multi-layer board.

Types of PP: Commonly used PP are 1080 (thickness 2.9-3.3mil), 1506 (thickness 6-6.5mil), 2116 (thickness 4.6-5.2mil), 3313 (thickness 4-4.2mil) and 7628 (thickness 7-8mil).

Core：The core plate is a hard, specific thickness, and double coated copper material.

The difference between PP and core：

1、 Prepreg belongs to a material in PCB, the former is semi-solid, similar to cardboard, the latter is hard, similar to copper;

2、Prepreg is similar to adhesive + insulator; The Core is the basic material of the PCB, and the two are completely different functions;

3、Prepreg can intertangle and Core can't.

4、Prepreg does not conduct electricity, while both sides of the Core have copper layers, which are conductive media for printed boards.

PCB stackup design

1、Preference for thin core with larger thickness (relatively good dimensional stability).

2、Low cost pp is preferred (for the same glass cloth type prepreg, the resin content does not affect the price).

3、A symmetrical stack up is preferred

4、Dielectric layer thickness > Inner copper foil thickness ×2

5、 It is forbidden to use prepreg with low resin content between 1-2 layers and N-1 /n layers, such as 7628×1 (n is the number of layers).

6、When 5 or more semi-cured sheets are arranged together or the dielectric layer thickness is greater than 25mil, the intermediate prepreg is replaced with a light plate except for the outermost and innermost layers.

7、The second layer and N-1 layer are 2oz base copper and the thickness of 1-2 layers and N-1 /n layer insulation layer < At 14mil, it is prohibited to use a single sheet of prepreg, and the outermost layer should use a high resin content prepreg, such as 2116 and 1080.

8、When a sheet of prepreg is used for inner copper 1oz plates, 1-2 layers and N-1 /n layers, the prepreg shall be selected with a high resin content, except 7628×1.

9、Plates with inner copper ≥3oz are prohibited from using single PP, generally not 7628, and multiple sheets of prepreg with high resin content must be used, such as 106, 1080, 2116.

10、For multilayer boards containing copper-free zones greater than 3 "x 3" or 1 "x 5", prepreg is generally not used between core boards.

Pressing often presents some problems and solutions

1.Blister

Solution：

1)、Increase prepressure, cooling, or shortening prepressure period;

2)、The pressure, temperature and fluidity are coordinated by the time-activity curve;

3)、Reduce the prepressure period and the temperature rise rate, or reduce the volatile content;

4)、Strengthen the cleaning operation;

5)、Increase the pre-pressure or replace the adhesive sheet;

6)、Check the heater match and adjust the hot die temperature.

2. The surface of the plate has pits, resins and wrinkles

Solution：

1)、Carefully clean the steel plate and smooth the surface of the copper foil;

2)、Pay attention to align the upper and lower plates with the plate when arranging the plate, reduce the operating pressure, choose a low RF% film, shorten the resin flow time and accelerate the heating rate.

3. Inner pattern shift

Solution：

1)、Use high-quality inner coated foil;

2)、Reduce the pre-pressure or replace the adhesive sheet;

3)、Adjustment template.

4. The thickness is uneven and the inner layer slips

Solution：

1)、Adjust to total thickness consistency;

2)、Adjust the thickness, choose the copper clad foil plate with small thickness deviation; Adjust the parallelism of the hot-pressing film plate, limit the freedom of the multi-answer sheet of the laminate plate and strive to place the laminate in the central area of the hot-pressing template.

5. Interlaminar dislocation

Solution：

1)、Control the characteristics of the adhesive sheet;

2)、The sheet is pre-heat treated;

3)、Use good dimensional stability of the inner copper clad foil and bonding sheet.

6. Board bending and warping

Solution：

1)、The design density of the wiring is symmetrical and the bond sheet is placed symmetrically in the lamination;

2)、Guaranteed cure period;

3)、Strive for consistent cutting direction;

4)、It would be beneficial to use materials from the same manufacturing plant in a composite mold;

5)、The multilayer plate is heated to above Tg under pressure and then cooled to below room temperature under pressure.

7. Heat stratification

Solution：

1)、Before laminating, bake the inner layer to remove moisture;

2)、To improve the storage environment, the adhesive sheet must be used up within 15 minutes after being removed from the vacuum drying environment;

3)、Improve operation to avoid touching the effective area of the bond surface;

4)、Strengthen cleaning after oxidation operation; Monitor the PH of the cleaning water;

5)、Shorten the oxidation time, adjust the concentration of the oxidation liquid or operate the temperature aromatic, increase the micro-etching, improve the surface state.