1. Abstract
In the world of electronic system design and development there is no greater milestone than the delivery of a working prototype. The integration of code, circuits and mechanical fit relies on a sequence of prototypes at various phases of system development. With PCB assemblies containing most of a products circuit and logic the PCB prototype is a key deliverable. PCB design tools are the means by which circuits are realized into PCB designs yet they offer little assistance to the operator of SMT assembly machines. The purpose of this paper is to describe how Index Designs has automated various stages of assembly machine setup to reduce the cost or prototype assembly and to improve the quality of the assembly process.

2. Hand vs Automated Assembly
If only 2 or 3 chips components require placement then nothing is faster than hand assembly. However as soon as BGA or .5mm pitch parts are introduced, or the number and type of components increases, hand assembly becomes a tedious and unreliable process.
The quality of soldered connections is primarily driven by solder paste placement. Using a stencil to place paste is simple but the hand placement of components onto paste, especially fine pitch parts, tends to smear paste resulting in shorts or leads with insufficient paste Assembly machines (pick and place) easily place components to within .001 inches and at very high speed. The problem with assembly machines relates to their programming and the setup of part feeders. If complete placement and feeding information can be
merged with a PCB design then prototype assembly using automated equipment is greatly simplified.

3. Required Data
Index Designs added 4 major attributes to its in house PowerPCB based design tools:

• Alignment from PowerPCB to Assembly
• Part Feeder Tables and Alignment
• Part Status and Placement Options
The amount of data required for a machine to locate a component, pick it up, align, transport and place is staggering. The nature of the data varies with machine type, version and installed options. Fortunately most machines provide a component ID (Part Number)
through which placement variables and libraries can be managed. The syntax of these IDs varies and conflicted with the “Functional Nature” of part numbers used at Index Designs. Business plans for Index Designs call for the driving of multiple machine types with different
tables used to drive different machines. While most PCB systems will export origin and
rotational information these parameters are almost never aligned with the target assembly machine. Index Designs generated several software tools to adjust placement data for BOM line items and then save those settings for use on future jobs. Placement data is shown to the user by rendering in house PowerPCB decal graphics over top of graphics extracted from Gerber files. The result is a “Software Pick and Place” that allows users to verify and correct placement data without the use of an actual placement machine.

Most designs contain line items that affect PCB design but do not require component purchase or placement. Additional line items might represent parts which are either not stuffed or they require hand placement. Attributes to control these operations can be placed in CAD tool libraries or maintained outside the schematic using a database. Index Designs selected the database scheme and incorporated placement control flags in its
BOM Builder application.

4. Part Feeders
The single greatest task involved with assembly machine setup is the logical and physical setup of the part feeders. Logical setup refers to the dividing of BOM line items into groups as required by machine feeder hardware. Physical setup refers to the placing of the
physical components into the mechanical feeders. With the feeders selected and loaded the machine operator must identify to the machine software which feeder locations contain which part types. When a board placement list is transferred to the machine and all part
types are programmed and loaded then assembly can start.

The TM8C reel feeders used by Index Designs require 4 minutes to load, trim and unload. If a job requires only 2 parts from a reel the cost per part is very high. Most jobs contain many 1, 2 or 3 part line items. It is common for a job setup to require the removal or addition of special feeder types. These feeders are often very expensive and their mounting increases setup time. When building only one or two boards machine setup quickly exceeds the time required to hand place and solder components. To reduce setup time an array of ustomized trays was designed to hold components.

Small quantities of loose components are easily placed in trays and short pieces of tape are placed on trays with tooling pins. A software “Tray Compiler” is used to take a BOM and map the components into trays. Additional software logic creates magazine definition files for the trays and these are downloaded to the assembly machine. A MyData TP12- UFP was equipped with a large “Tray Wagon” and tooling has been added to hold trays in know positions.Information associated with parts can be kept with standard CAD attribute fields or within a parallel database. While storage within attributes is easy to implement the storage within a database simplifies the writing of management software. A database was constructed that contains the definitions of standard trays. Tray definitions consist of arrays of holes located in X and Y. Each hole has an associated depth. Multiple trays of the same size and shape can exist and each tray is given a serial number.Multiple BOMs are merged as part counts are multiplied by the number of boards being built. As the count of a single part exceeds a threshold then, as feeding information permits, feeding varies from loose parts to strips of tape to reels. The goal of this process is to minimize job setup time.