Component placement

In component placement and soldering several restrictions must be considered, as shown in Eigure 42. 

Conventional printing processes are less useful for applying conductive adhesives or solder paste. Dispensing of single dots in a complex geometric application is therefore necessary. Three-dimensional circuit carriers also decrease the freedom of component placement, which leads to restrictions for placement systems. 

High green strength to hold components in place during component placement and reflow soldering. 

Table 4.19 Effect of adhesive viscosity on dispensing and component placement time ...

The number of dots that can be dispensed per unit of time also depends on viscosity. The use of low-viscosity adhesives increases the number of dots that can be dispensed. However, there is a tradeoff between the speed at which the adhesive can be dispensed and the speed of device placement. Most automated component-placement equipment operate faster than adhesive-dispensing equipment. A comparison of the effect of viscosity on dispensing and placement times is shown in Table 4.19 for an 86-lead plastic-encapsulated leadless chip carrier (PLCC). ... 

A wide variety of fully automatic machines exist. Generally, feeders, which may consist of tape-and-reel, stick, or tray, deliver the parts individually so they can be picked up and automatically inspected. Machines are equipped with vacuum nozzles to pick up the components and carry them through inspection, alignment, and placement. A list and description of commercially available component placement equipment is given in Table 4.24. 

High shear thinning and flow under pressure with quick recovery and limited flow after component placement (good thixotropic properties)... 

Table 4.19. Effect of Adhesive Viscosity on Dispensing and Component Placement TimeP ...

Component placement places the registers and FUs in order to reduce the connections. Because Amical uses a bus-based target architecture, the placement of registers and functional units is very important. Optimal placement will minimize the number of busses necessary. 

FU allocation is based on an EMUCS-like algorithm [5]. Micro-scheduling uses an ASAP algorithm. Component placement and connection allocation make use of improved constructive approaches similar to those used in APOLLON [6]. The originality of the approach is that all of these algorithms are implemented in order to allow mixed manual and automatic design. With the exception of micro-scheduling, they all use a constructive approach. At each step, a new element is allocated or placed. The four steps may be sequenced automatically or performed step by step. Each step may be executed automatically, interactively, or manually. 

Surface mount techniques have also been successfully used to assembly hybrid circuits. The metallized ceramic substrate is simply substituted for the conventional printed circuit board and the process of screen printing solder, component placement, and reflow solder is identical. 

---