Via hole punching

In the manufacture of the multilayer structure for the TCM, square sheets are stamped from a roll of green tape loaded with a debased alumina powder. Many small (about 150 /im diameter) holes ( vias ) are punched through the tape at predetermined positions. Electrical wiring patterns with line widths and... 

For many years, nearly all the substrate materials used in the electronics industry were ceramics produced by tape casting (Mistier, 2000). These substrates consist of multiple layers of tape-cast material acting as the insulative carrier, with layers of metal deposited by sputtering, CVD, or evaporation processes. Holes punched into the tapes fill with metal and act as vias or pathways between layers when the tapes are stacked. Stacked layers of tape-cast blanks are laminated together and then sintered to produce a monolithic substrate. This process is detailed in many handbooks on electronics packaging (e g., Harper, 2000). One of the prime benefits is that the layers of the final part can be different different hole patterns, different metallization patterns, even different dimensions on each layer. 

In addition to punching or piercing through holes, punch press tooling and computer numerical controlled punch press machinery are very effective in creating sheet metal parts with formed features. Some examples of features produced via forming operations are as follows ... 

Via holes larger than > 0.5 mm (0.020 in.) are usually very easy to form, since materials such as tungsten carbide can be used as punching tools. For smaller holes, in the range of 0.25 mm or less, tungsten carbide may be too brittle, and other materials such as borided tool steel should be used. There are several companies that boride the tool steel punches that have been machined to size. 12 This process yields a punch with the surface hardness of a carbide but with some flexibility. 

Transfection efficacy of naked DNA can be increased by physical methods such as electroporation and sonication. Electroporation employs electric pulses to punch holes in the cell membrane, usually smaller than 10 nm but larger than oligonucleotides. With the use of electroporation, DNA was delivered into the cytosol of cells by diffusion. Since its introduction in 1982, in vivo transfection has been achieved in skeletal muscle, fiver, skin, tumors, testis, and the kidney. Tsujie et al. (2001) developed a method to target glomeruli using electroporation in vivo wherein injection of plasmid DNA via the renal artery was followed by application of electric fields. The kidney was electroporated by sandwiching the organ... 

A series of proteins collectively called the complement participate in the immune response to the entry of foreign cellular or viral material into the organism. This group of proteins consists of about 20 entities, some of which are enzymes. Complement was first associated with the lysis of foreign red blood cells in the nineteenth century it also participates in the lysis of bacterial cells. The complement activation cascade, very similar to the blood coagulation cascade, involves the stepwise activation, via proteolysis, of various components of the complement system until a final protein complex, the membrane attack unit (also called the C5b-9 complex), is generated. It then punches holes in the membrane to which it is bound. 

The green tape can easily be punched to produce holes or vias, which are an important part of the processing of 1C packages. In... 

The green tape is furnished in a roll or as precut squares approximately 3-12 in. on a side. The first step is to cut four alignment holes with a punch or laser in each comer followed by cutting holes for vias and other requirements. The punch is preferred for high-volume applications whereas the laser is best for prototypes. The most common via size is 250 pm, with vias as low as 100 pm being possible [8]. This is about half the size attainable by conventional thick-film technology. 

A framed piece of E>upont 951 LTCC after the via punch process. The holes in the tape, as well as in the stainless steel frame, are commonly used for registration of layers. 

Once each of the blanked tape layers has been prepared for use in a substrate, the first process is normally via and cavity formation. In this process, the individual holes through each layer of the green ceramic are formed to allow electrical connections between layers in the vertical axis of the substrate. In addition, channels or cavities can also be punched or cut into tape layers to form a wide variety of unique electrical and mechanical features within a substrate. Traditionally, cavities have been used to recess integrated circuits into the ceramic to allow their siuface to be flush with that of the ceramic or a wire-bond ledge. This approach is still popular and has a number of electrical and in some cases mechanical advantages when compared to placing the devices on the ceramics siuface. In the past few years, these processes have also become very popular for the creation of unique electromechanical structures within the ceramic substrate such as those used for MEMS devices. 

---