Drilling Processes Laminate

For decades, the majority of PCBs have been built with epoxy resins, dicy-cured, and with bromine flame retardant.The industry has developed around this paradigm. Drills and drilling, chemistry, lamination, and circuit card assembly are all well understood with reference to standard FR-4. Although there are fabricators with processes developed to manufacture PCBs using laminates other than standard FR-4, this knowledgebase is not distributed industrywide. Especially problematic is the intersection of requirements for HF and/or LFAC with high thermal resistance and improved electrical characteristics, such as low attenuation in the material. 

Figure 63.2 shows standard manufacturing processes of the through holes for the doublesided flexible circuits. A mechanical numerically controlled (NC) drilling process on double-sided flexible circuits can be done similarly to that used for rigid double-sided printed circuit boards. More laminates can be stacked up in the setup because of the thin materials. 

Changing laminates also affects drilling processes. Higher thermal laminates require variations in drill feed and speed rates. Some have different chip-load requirements, others need different bit geometry. Meanwhile, lower drill-hit counts may be required to maintain quality. Changes in hit counts and feed rates could also increase processing time. 

Some of the procedures of value for processing of mixed plastic wastes may also be useful for the recovery of value from the laminates used for efficient packaging of food and beverages (e.g., milk cartons, Tetrapaks). A combination of heat and pressure may be employed on a recycle stream of this type of material to fuse the mixed fibrous and resin components into a dense board-like product [31, 32]. This highly weather and insect resistant product, Eco Superwood Plastic Lumber, may be sawn, nailed, drilled, etc., like wood, and it resists rotting in direct contact with the soil without the need for preservatives. 

The transistor film is then mechanically processed by a numerically controlled (NC) cutting plotter or drilling machine to form the net-shaped structures, as shown in Figure 6.3.8. In a similar way, a pressure-sensitive rubber sheet and a copper electrode suspended by a polyimide film are cut separately to form net-shaped structures. These two films are laminated on the top of the transistor fihn to complete the pressure sensor network. The periodicity is 4 mm, and the width of the struts is 0.3-0.5 mm. 

The purpose of copper pads surrounding the drilled holes in PWBs is to accommodate any potential layer-to-layer or pattern-to-hole misregistrations and thus prevent any hole breakout outside the copper area of the pads. This misregistration is caused mainly by the instability and movement of the base laminate during its processing through the PWB or multilayer board (MLB) manufacturing steps. 

These blends include epoxy-polyphenylene oxide (PPO) (see Fig. 7.7), epoxy-cyanate ester, and epoxy isocyanurate (see Fig. 7.8). While these materials have been developed to minimize impacts to common printed circuit manufacturing processes, they can affect productivity in multilayer lamination and drilling and can require special desmear and hole wall conditioning processes, depending on the design of the printed circuit and fabrication process used. On the other hand, they typically have less of an impact to these processes when compared to the even higher performance materials. 

Material Utilization. The material manufacturing costs, which correspond to 30 to 40 percent of total costs, are directly related to the sqnare inches of material processed.The material costs can include the following laminate, prepreg, copper foil, solder mask, photoresists, drill bits, chemicals, and so on. Generally, these materials are consumed relative to the panel area manufactured. 

Layer pairs are prepared using conventional processes of etching, plating, drilling, and so on, or by conductive paste processes. The layer pairs are laminated together using B-stage resin systems or some other form of dielectric adhesive into which conductive paste vias have been placed. 

Circled processes 3,4, and 5, as well as squared 3 through 10 in Fig. 23.1, utilize a laser drill via generation technique. This process was first used in the late 1970s to drill small holes in G-10 laminate for buried vias in mainframe computer boards by IBM for its 3081 system and by Burroughs. (Attempts to find pictures of these products proved unfruitful.) The Hewlett... 

PPBU. The PPBU (Prepreg Build-Up), from CMK, is a standard sequential lamination process using laser-drilled vias similar to the CLLAVIS process. The diagrams in Fig. 23.17 show two of the structures, a standard 2-i-4-i-2 build-up and an advanced 3-I-2-I-3 stacked build-up. 

Definition. The maximum hits per tool specified for any given drill size implies the number of drill strokes a drill bit is used for until its expected effective life is expired. Maximum hit count per tool is product and process specific and is affected by laminate material construction, panel thickness, drilled stack height, surface speed, and the type of entry and backup material used. Therefore, no specific number of hits per tool can be arbitrarily specified. 

These changes fundamentally impact the fabrication of the base materials into ML-PWBs especially in the lamination, drilling, and hole-preparation processes. The process impacts will be discussed in later sections. 

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