Issue link: https://iconnect007.uberflip.com/i/1523825
42 DESIGN007 MAGAZINE I JULY 2024 Factory Initiative Subcommittee was formed. e ultimate goal of the subcommittee was to develop soware tools that relied on a single, comprehensive, agreed-upon language and data set for all machine types. e Connected Factory Exchange (CFX) was born: "Implementing CFX eliminates need- less machine interface development costs, elimi- nates the need for middleware and reduces time, risk, and costs for solution deployment." 1 SMT Assembly Sequence Step one: Solder deposition is the process of printing a precise volume of solder paste onto the land pattern features of individual com- ponents. e base material commonly used to prepare the stencil is a thin stainless-steel sheet. Land pattern features are laser cut using a program developed directly from the circuit board design file to form the openings for sol- der paste transfer. Solder alloy compositions selected for surface mount assembly typically combine tin and silver or tin, silver, and copper (Sn/Ag/Cu). e Sn/Ag/Cu combination has become the alloy of choice for a broad number of commercial electronics assembly applica- tions. e so-called SAC alloys provide excel- lent solder joint reliability, fatigue resistance, minimized copper dissolution rates, and all elements within the compound comply with IPC, JEDEC, RoHS, and REACH lead-free (Pb-free) soldering standards. To enable precise alignment of the sten- cil and circuit board, two globally positioned fiducial targets will be provided on the cir- cuit board's surface. To accommodate camera access for stencil-to-board positioning, these target features will be partially etched into the bottom surface of the stencil panel. Step two: Component placement employs robotic systems with vacuum pickup nozzles, using the coordinates and orientation furnished in the PCB design file to sequentially pick up each component from a carrier and place it onto the designated land pattern feature on the circuit board's surface. Placement systems have taken on a modular approach, with larger and smaller components assigned to different modules that are appropriately tooled. When circuit boards have a high quantity and wide value range of small passive components, two or more modules may be required. Because most surface mount components are passive resistors and capacitors, the machine selected for assembly of these devices is likely to implement a high-speed "chip placer," reserving the slower but significantly more accurate placement system for mounting the larger, high I/O lead-frame and BGA semi- conductor packages, the smaller fine-pitch BGA devices, and even WLCSP (face-down bumped die elements). Placement system selection criteria: • Number of components • Number of component values or types • Component complexity (fine-pitch) • Placement accuracy and repeatability Although component placement speed is important, assembly systems may have differ- ing levels of accuracy. e more complex and significantly heavier semiconductor devices will have a slower cycle time and will require vision capability to ensure component-to-land pattern alignment accuracy. e following criteria for component place- ment accuracy will influence assembly system selection: • Passive devices: ±70 micron • Small outline ICs: ±70 micron • Fine-pitch ICs: ±40 micron • BGA and FBGA: ±40 micron • Flip-chip/WLCSP: ±20 micron As passive components become smaller and terminal pitch on semiconductor packaging shrinks, placement accuracy will be even more critical and precise. Step three: e last step of the surface mount assembly sequence is the solder-reflow pro-