What is the prospect of the ceramic PCB industry

Taking a little time to introduce new words and concepts of flex-rigid boards will help to clarify the complex manufacturing process. A typical flex-rigid board has two sets of hard cover plates made on the upper and lower surfaces of the circuit board, and one or more layers of FPC are sandwiched in the middle. . The cover plate and FPC will be firmly attached together and extend to the hard area, which is the part containing the PTH. The soft board layers may be attached to or separated from each other in the areas that need to be soft. The choice depends on the relative deflection requirements or the manufacturing cost.

Most of the cover plates are not made into a multi-layer structure in advance, but are made into a standard single-sided circuit double copper panel, which is constructed by laminating copper sheets or cover plates during multi-layer lamination. The method of copper sheet lamination includes a layer of film on top and a copper sheet to construct the outer surface of the rigid-flex board. The cover plate lamination process is similar to the general lamination process, but the original copper layer is replaced by a single-sided all-copper circuit board substrate. Both processes can be used in the traditional double-copper surface cover plate process to deal with single-layer or Rigid-flex board manufacturing process of other structures.

Before the FPC stack enters the press, the cover plate, each part of the flexible board, the film or the connecting adhesive will be punched by tool hole, windowed, slotted and partially formed to generate the non-adhering area or the outline edge. It is the most difficult part of the final soft and hard board.

The fenestration part is made with a knife die, which is aligned with the adhesive or film layer by means of tool holes and latches, and precisely cut out specific areas. The same process is also used to create the filling material, which has the same thickness as the adhesive, such as Teflon, Tedlar or TFE-glass cloth. However, most of the processes currently used by the industry do not add fillers to save manpower. However, in the lamination process, they will face the problems of fracture in the fault zone, gradual thinning and tilting of the thickness at the junction, and inability to completely control the flow of the film. Infill is the area that protrudes into the fenestration when stacked, and functions to:

(1) Restore the thickness of the stack to achieve a uniform pressing pressure

(2) Avoid bonding between FPC layers

(3) Lock the flow of the adhesive (or film)

(4) Keep distortion to a minimum

The cover will be pre-grooved along the edge of the area where the FPC needs to be exposed. If the cover is not grooved before pressing (or nicked inside for breaking), cutting this edge in the final product requires quite specialized and Precise Z-axis control to avoid damage to the FPC.

The edge of the FPC layer may not be attached to other parts in the final product, so it is very difficult to cut. Most of these parts will be partially cut in advance with a knife die. Scrap products will not be cleared before pressing, and nothing will be cleared. The FPC layer will enter the process as a whole, and the tool system in the edge and scrap area will be used to assist alignment and thickness control.

If it is actually necessary to generate a multi-segment structure in the PTH region, a sequential lamination process must be used. With this technique, the layers of the thinner areas are first finished and PTH processed before being introduced into the final flex-rigid stack. At this time, the area where the PTH has been completed is sealed with an additional soft board and cover layer inside the thicker soft and hard board to establish the final thickness for the second PTH process.

In the unattached part of the hard zone, if it is too large, it may swell during plasma treatment and cause layer separation, which must be determined by the overall sealing and the amount of free play contained. When the FPC bend area exceeds 4 to 5 square inches, the force of expansion is generated in the hot, vacuum plasma process, which can pull the edge of the cover. Faced with this situation, it is sometimes possible to create vents first to relieve pressure in these areas, which may pull the edge of the cover off. Faced with this situation, sometimes it is possible to make vent holes to release pressure in these areas, but it must be sealed before the PTH process.

Rigid-flex boards require particularly stringent quality control, and perhaps the most challenging inspection procedure is thermal stress, which may require visual and cross-sectional analysis of representative PTH coupons. The coupons need to be baked at 125°C for at least 6 hours before cooling, fluxing and tin bleaching at 288°C for 10 seconds. The surface is then inspected for defects such as: abnormal woven fibers, exposed fibers, scratches, ring separation, dents, indentations, and then sliced to analyze the overall condition of the electroplating and the broad characteristics of the soft and hard areas.

A general habit is to first examine the pad and trace area adjacent to the PTH hole, and then examine the location along the trace extending to the next PTH hole. One of the more common soft and hard board quality problems that cause rejection is substrate voids in the extension area. These are voids or air bubbles in the dielectric structure. Generally defined, as long as the substrate voids are greater than 3mil or interfere with the space between the conductors was rejected.

Some applications require very severe bending in the soft board area, and the gradient design will be used to reduce the stress in the assembled state (but it must be assembled through a rather complex process and high stress welding). Progression is a design technique used in the FPC layer. The order of bending in the bending area is from the inside to the outside, and it will gradually increase to compensate for the increased channel length.