For the production of core boards, press-fitting is the most important process. There are many problems in the production process that are worthy of research and discussion, such as: wrinkling of copper foil, bias of laminated layer, void of resin, white corner of white edge, layered foaming, uneven thickness, etc.
In order to solve the above problems, it is necessary to have a clear understanding of the control points of the main material (inner core board, PP) and the press, and to be familiar with its characteristics.
Second, The Main Material of The Core Plate Pressing Process
A. Inner core board
The multi-layer core board which has been etched to form the inner layer pattern is called the inner layer core board, and the inner layer core board must be subjected to brown (black) treatment before pressing, in order to increase the surface of the inner layer copper foil. The roughness makes the PP sheet flow glue fully bonded to the copper surface during the pressing process, so as to increase the bonding force between the PP and the copper surface.
As the level of the multi-layer board becomes higher and higher, the inner core board becomes thinner and thinner, and the horizontal browning process gradually takes the vertical blackening process, confirming whether the browning effect of the inner core board meets the requirements, mainly from three Aspects: micro-etching, acid-fastening time, browning tension.
B. Prepreg (PP):
Commonly used PP sheets are mainly composed of epoxy resin and glass fiber;
2. The main basic physical properties: The amount of glue RC%: the proportion of epoxy resin, can be tested according to the test method of IPC-TM-650 2.3.16;
gel time GT: the time required to test the B-stage PP sheet to complete C-stage curing at 170 ° C, can be tested according to the test method of IPC-TM-650 2.3.18;
volatiles V.C%: test the residual amount of solvent in the PP sheet after the impregnation process, can be tested according to the method of IPC-TM-650 2.3.19;
as a medium combined with the core board and the core board, the core board and the copper foil;
Impedance Control: Provides a thickness that provides a suitable insulating layer;
At present, the main PP sheets used are 106, 1080, 3313., 2116, 1506, and 7628. PP sheets of different specifications and the same specifications, different amounts of glue, and different thicknesses of the press.
5. Storage Conditions:
Humidity: ≤50% RH;
Temperature: ≤ 5 ° C: can be stored for 180 days; 20 ± 2 ° C can be stored for 90 days;
Third, Press Equipment
1. Type of hot press:
According to the different heating methods, the main types can be divided into:
electrothermal heating: This is an early heating method, but because the lifting temperature is unstable, it is rarely used;
Hot kerosene heating: The heat medium oil is heated by the boiler, and the heat is transferred to the press by the heat medium oil. Because the heat provided is stable, it is easy to control in the temperature rise and fall. At present, most presses adopt this heating method.
2. Pressure pressure method:
At present, most presses use hydraulic pressurization, and the pressure source is from the bottom up cylindrical cylinder.
3. Control points:
-Vacuum: After the press is started, it is vacuumed before starting to press, to avoid air bubbles remaining during the pressing process;
-Time: the temperature and pressure slope and holding time of each stage, mainly affecting the heating rate and curing time;
-Pressure: The pressure on the production board at each stage mainly affects the flow glue and stress release of the production board;
4. Temperature: the temperature of the hot plate of the press at each stage mainly affects the actual temperature of the production plate;
Fourth, The Quality of The Focus After Pressing:
1. Reliability of the Production Board:
-Thermal stress: measure the heat resistance of the production board, test method: thermal shock (288 ± 5 ° C, immersion tin 3 times, 10 Sec / time);
-TG; measure whether the PP of the production board is completely cured, test method: IPC-TM-650 2.4.25 DSC
-Peel strength: measure the bonding strength of copper foil and PP on the production board. Test method: IPC-TM-650 2.4.8
- slice measurement of the thickness of each layer of dielectric layer;
- Use the thickness gauge to measure the thickness of the edge of the board and the thickness of the board, generally measuring 5 points or 9 points;
-Appearance: no pit dents, copper foil wrinkles, white edges and white corners
The abnormality caused by the pressing process of the core plate is generally found after the outer layer is etched (especially the resin void, white edge white angle). At this time, the production time of the production plate has exceeded 3-5 days, and the abnormal tracing It's more hot. According to past experience, the abnormality is mostly caused by process operation or abnormal materials and equipment. Therefore, in daily operation and control, it must be completely implemented in accordance with WI standards. For the inspection and inspection of equipment, it must be completed regularly, and abnormal shutdowns should be stopped in time. Never take sick work.