Surface-mount technology

5 m/sec to 20 m/sec result from starts and stops in automated handling equipment. Thus, high green strength is necessary to maintain component orientation prior to soldering. 

Green strength may be determined by measuring the lateral force that bonded parts can withstand. In one test method (Siemens Standard SN5965a populated board is allowed to slide down an incline to a stop at the base, and the displacement of components on the board is measured (Fig. 5.4). An acceleration run of400 mm from a height of 35 mm is made. A maximum shift of0.15mm(50%of the track pitch for a standard 0.3 -mm pitch part) is considered acceptable. 

Optional and not required if adhesive cures in preheat zones of a reflow oven. 

After the solder has been reflowed and the adhesive has been cured, the adhesive has served its primary fimction of holding the components in position during solder reflow. However, since the adhesive remains permanently on the board, its cured properties must be such that it will not reduce the reliability of the assembly or cause subsequent failures. 

Product Name/ Supplier Type Viscosity cps Thixo- tropic Index Yield Value (N/m Casson) Shelflife -40 C/ Pot Life 25 °C Cure Schedule min °C Lap- Shear Strength psi CTE ppm/°C °C Volume Resistivity ohm-cm Thermal Couductivity W/m-K 

Multichip packaging involves the attachment and interconnection of a variety of chip devices on an interconnect substrate that may be single layer or multilayer. There are two basic types of multichip packaging hybrid microcircuits and multichip modules. 

The key PCB material requirements include high mechanical strength and modulus, durability and toughness, chemical resistance, flame retardance, a compatible CTE with the PCB, dimensional stability and ease of processing, and many LCPs can meet all these stringent requirements. 

The CTE is unique in being extremely low, and can be tailored to meet specific component requirements by careful selection of fillers and additives, and through part design, mould design and gate location. This characteristic has already been exploited commercially in couplers and connectors for fibre optics. 

Testing has taken place to compare LCPs with two materials used widely for electronic and telecommunications components glass-filled polyphenylene sulphide (PPS) and glass-reinforced polybutylene terephthalate (PBT). Over the temperature range 50-200 °C, the CTEs for the connectors made from the different plastics were 11 ppm/°C, for 

Clearly, it is important that the CTE of materials used in the production of components for surface mounting should match the CTE of substrates as closely as possible. The through-hole assembly process currently allows a level of imprecision and CTE mismatch since any differential expansion can be accommodated by the compliance of the component leads. Much greater precision is required in surface mounting, where any difference in CTE between mating parts can result in failure due to poorly controlled part-to-part dimensions, stressing of components, device or board damage, or poor solder joints. 

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Multilayer boards, which use multiple interior laminates of plastic and copper, now comprise over half of the value of production, though much less on a surface area basis. Surface mount technologies demand extreme flatness and reproducibiHty from surfaces. Greater packing density has led to commercial production of finer lines and holes, often less than 50 p.m and 500 p.m, respectively. Electroless gold over electroless nickel—phosphoms, or electroless nickel—boron alone, is often used as a topcoating for wire bonding or improved solderabiHty. 

Except for some exotic surface-mount technology (SMT/SMD) aluminum electrolytic capacitor types with solid electrolyte systems, in general, an aluminum electrolytic capacitor contains a wound capacitor element (the coil), impregnated with liquid electrolyte, connected to terminals, and sealed in a can (with a rubber plug at the end). The aluminum in the name,... 

We should not think that heat is lost only from the copper side. The usual laminate (board material) used for SMT (surface mount technology) applications is epoxy-glass FR4, which is a fairly good conductor of heat. So some of the heat from the side on which the device is mounted does get across to the other side, where it contacts the air and helps reduce the thermal resistance. Therefore, just putting a copper plane on the other side also helps, but only by about 10 to 20%. Note that this opposite copper plane need not even be electrically the same point it could for example just be the usual ground plane. A much greater reduction of thermal resistance (by about 50 to 70%) can be produced if a cluster of small vias (thermal vias) are employed to conduct the heat from the component side to the opposite side of the PCB. 

The class of polyester-based liquid crystal polymers (LCPs) represent one of the most attractive materials in the field of engineering thermoplastics because of their superior mechanical properties, heat resistance, accuracy of dimensions, moldability and the excellent balance of these properties [1-5]. LCPs have been recently expanding their applications, in particular, those for precision electronic parts appropriate for surface mount technology (SMT). 

PCX withstands SMT (surface mount technology) reflow soldering. 

Surface Mount Technology International Society for Hybrid Microelectronics Silver Spring, MD, 1984. 

Surface Mount Technology (SMT), A Compendum of Technical Articles Presented at the First, Second, and Third Annual Conferences International Electronics Packaging Society Glen Ellyn, IL, 1984. 

The electronic unit of the LAPS device can be created on a double-sided printed circuit board with the help of surface-mounted technology to bring it as close as possible to the sensor chip. The integrated electronic unit enables an easy access to the different measurement spots and provides an amplified, filtered and easily measurable (converted) voltage signal (several V) with respect to the sensor signal (several pA). The electronic unit contains different blocks, which are described in Fig. 6.2. 

Morris JR, WojcikT (1990). Soldering Surface Mount Technology, No. 5. 

As resistive heating elements of this electrothermic interface thin film platinum resistors and surface mount technology (SMT) resistors are used (Richter et al. 2003, 2009a). The hydrogel components can be heated and cooled also by Peltier elements (Yu et al. 2003b Luo et al. 2003a). 

In recent years the industry has been driving toward surface mount technology over through-hole mount technology. This is more demanding thermally and requires materials to be formulated... 

Automotive connectors have many of the same demands of high heat surface mount technology connectors. Examples of blends and alloys in these applications are largely based on PBX and PA-66. Xhe high heat and high solvent resistance requirements make a semicrystalhne resin a suitable choice. Xhese systems include ... 

Siemens AG (1999), The World of Surface Mount Technology, Automation Technology Division, Siemens AG, Munich. 

Surface-mount technology replaces previous methods of inserting component leads into plated through-holes of PWBs, wave soldering from the back side to flow solder into the holes, and simultaneously forming both mechanical and electrical connections. SMT is highly automated and currently the most widely used production process for the assembly of single-layer, double-sided, and multilayer circuit boards. 

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