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An integrated methodology for surface mount PCB configuration
Computers ind. Engng Vol, 35, Nos 1-2, pp. 53-56, 1998
Pergamon
© 1998ElsevierScienceLtd. All rights reserved Printed in GreatBritain PIh S0360-8352(98)00018-7 0360-8352/98$19.00+ 0.00
AN INTEGRATED METHODOLOGY FOR SURFACE MOUNT PCB CONFIGURATION
Zhongkai Xu, Ken Carlson and Richard Kurschner
Sabah Randhawa
Board Build Operation Tektronix, Inc. Portland, Oregon 97077
Oregon State University Corvallis, Oregon 97331
and Man
r
Engmee
ABSTRACT An integrated methodology for surface mount printed circuit board assembly configuration is described. The methodology involves component-to-feeder assignment, feeder bay distribution among components, board family formation, and machine program generation. Applications result in significant reduction in setup times and in planning and scheduling times. © 1998 Elsevier Science Ltd. All rights reserved.
KEYWORDS Surface mount technology; PCB assembly; component allocation; placement sequencing.
INTRODUCTION The manufacturing of printed circuit boards (PCBs) is a major activity in virtually every segment of electronics manufacturing. The sequence of activities involved in PCB assembly include: • • • • • • • •
Receive board design and specifications from customers. Design component placement control programs, tooling, and fixture. Acquire raw PCBs and components. Schedule production of boards. Screen printed solder paste on to boards. Place surface mount components on boards. Reflow solder assembly. Place through-hole components and connectors. • Wave solder assembly. m Perform board testing. The focus of the research reported in this paper is directed at Surface Mount Technology (SMT) which is increasingly being used in the design and manufacture of PCBs. The placement of surface mount components is a key task in the assembly of PCBs. Surface mount equipment manufacturers generally design equipment for high speed operatiens. However, due to high mix of components and small batch sizes characteristics of many low-volume manufacturing environments, up to 70 percent of the production time can be spent on machine setups. Practices that minimize setups can significantly enhance system productivity. 53
23rd International Conference on Computers and Industrial Engineering
54
SURFACE MOUNT OPERATION At the start of a new production run, the appropriate assembly programs are loaded into a surface mount machine's controller. The PCB is transferred to a registered position and secured. The positioning system adjusts the pattern coordinates of the PCB. The placement head is then moved to the designed feeder location to pick a component. With the aid of a vision system the component is lead to the board site and the placement position is adjusted. The component is then placed on to the board. The pick and place process is repeated until all required components are inserted. The PCB is then released and transferred to another head or to the next assembly station. A typical pick and place machine has three control components: Process control, machine control, and supporting databases. The process control component retrieves the data needed for the placement process from the database in real time. It also checks if pre-placement activities are required, for example, presentation of new components. The machine control component is responsible for the control and monitoring of all activities associated with machine operation. This includes positioning of carriage with the required components and the operation of tape feed and tape cutters on the feeders. Finally, the databases store the information required during a placement cycle. This includes information about the machine, feeders, components, and placement programs. The decisions resulting l~omthe interactions among these three components can be divided into three levels:' •
Grouping-Selection of machine groups and part families and assignment of families to groups.
•
Allocation-Allocation of components to machines when a group has more than one machine.
•
Sequencing-arrangement of component feeders and sequencing of placement operations for each machine and PCB assembly.
Implementation of these decisions depend on the component technology and capability of the system, and product characteristics.
METHODOLOGY The objective of this research was to develop a systematic and practical methodology for machine feeder assignment decisionsto reduce machine setup times. A unique feature of this methodology is its integration o f c o ~ t - t o - f e e d e r allocation, feeder bay distribution for machine carriers, and automatic PCB program generation. The methodology consists of four major components: Component-to-feeder assignment, Fixed feeder bay allocation, board family formation, and machine program generation.
Component-to-Feeder Assimunents The first step in the placement process is installing of components into feeders. A feeder may have one or more tracks and each track can hold only one ~ t . Multiple feeders can hold one or more components of the same type, i.e., different types of components can not be mounted into the same feeder. Two small components, 8 mm for example, can be simultaneously mounted into a double feeder.
tMcGinnis, L.F., et al. (1992). Automatedprocess planning for printed circuit card assembly, liE Transactions, 24(4), 18-30.
23rd International Conference on Computers and Industrial Engineering
55
A common practice for component-to-feeder assignment is based on comixDmt-board usage. Two ~ may be nssismd to a donble feeder if tbey have a similar board usage. This method may place two comp(mm~ with same board usage into a double feeder, but the two congxm~ts may belong to two different board families, resulting in wasted feeder space and increased machine setup time. This methodology uses a similarity measure for each pair of oomponents. The similarity measure is based on a component-board incidence matrix that defines the set of componmts required for each board. The assignment of components to feeders is determined by formulating and solving a 0-1 integer programming problem, where the objective is to maximize the sum of component similarities.
Fixed Feeder Bav Determination Prior research has focused on arrangement of different machines into manufacturing cells and the selection of the component types to allocate to each machine on the basis of similar processing requirements to produce one or more families of PCBs. This implies that boards with similar components will have similar machine configurations or setups. However, this is not always the case. Generally, setup for a board is based on a pre-configured machine program and configuration file for that board. Before a new PCB is assembled, all cmgmnmts must be in the feeders on the preassigned feeder locations on the machine carrier. When a new PCB arrives at a machine, if the madfine does not have all the components needed for this PCB and/or the needed ccantxme~ are not in the preassigned locations on the carrier, a new setup of component feeders will be required. This methodology divides the machine carrier into three different feeder bays: fixed, semi-fixed, and configurable. Logically, commonlyused componentsshould be placed in the fixed feeder bay in order to minimize the machine setup time. In most cases, the componeats allocated to the fixed feeder bay will not be removed (hence, no feeder changeover is necessary in this area) unless additional feeder spaces are required from the fixed feeder bay for large PCBs. It is assumed that the machine carrier has enough capacity to hold all the components of any single PCB, but not the total number of components for all the boards (in a planning horizon). This implies that the fixed feeder bay cannot take all the feeder locations on the machine carrier. To determine the capacities of the three feeder bays, a cost-benefit analysis is used to determine the breakeven points between the three categories. The analysis explores the trade-off between the benefits of adding additional components, say to the fixed feeder bay, versus the costs of taking one or more components off the fixed feeder bay due to inadequate capacity outside this bay.
PCB Family Formation The result of the first two steps in this methodology is to create a master feeder setup for all PCB types in the fixed feeder bay. As a result of using this master feeder configuration for all the boards, generally no feeder changeover is needed within the fixed feeder bay. To further enhance similarity within the boards, the boards are further divided into famih'es to minimize setup within families. Board families are kept together during board sequencing in order to reduce both the machine setup time and simplify daily scheduling operations. Usually, a board family would contain a variety of board types requiring a large number of components. However, a board family shares many common component types. The cost-benefit analysis of the previous step and the board families in this step result in pattifiening of the machine carrier into: (1) Fixed feeder bay that holds most of the ~ ~ for all the PCB types; no feeder changeover is needed within the fixed feeder bay unless there is inadequate feeder capacity for large PCBs, (2) Semi-fixed feeder bay that holds conanen ~ within board families; the feeders are fixed within a board family but changeover is required between board families; and (3) Configurable feeder bay that holds the remaining components which cannot be placed into the fixed or semi-fixed feeder bays.
56
23rd International Conference on Computers and Industrial Engineering
PCB Machine Prot,ram Generation Once the fixed feeder bay is determined and the board fatuities are formed by the partitioning procedure described in the previous sections, the correspondlnS machine configuration and programs for each board are generatedthrough a machineprogram generator or optimizer. A master machine configuration is created based on the components allocated to the fixed feeder bay. This is followed by a group configuration file for each board family based on the ~ assismd to the semi-fixed feeder bay for that gronp. Finally, the machine configuration file for a board is generated from the group configuration files. The machine program generator, interfacingwith appropriate database, automatically generates these configuration files. This greatly speeds up and simplifies the machine program generation process and provides a repeatable procedure for PCB configuration that is responsive to a dynamically changing manufacturing environment.
CONCLUSIONS This methodology was applied to a large sample of industrial data involving thousands of components and hundred PCBs on two surface mount machine production fines. Machine carrier capacity of these lines was 300 feeders with each feeder capable of holdinga singlec o ~ t except for double feeders which can hold two 8 nun components. Comparison with a previously used spreadsheet-based tool showed a 60 percent increase in similarity value obtained in component-to-feeder assignment. After components were assigned to feeders, the machine configuration files were generated. Evaluation across all experimental conditions showed the proposed methodology to reduce the machine setup by approximately 15 percent. Actual production d~t~ gathered over several weeks is also consistent with the results of the simulation evaluation. Furthermore, by creating integrated computer modules for the methodology described above, the time to regeneratemachine programs for a new production line configuration is reduced from weeks to days. This is critical in today's manufacturing environment where the product mix is continuously changing and responsiveness to changing market needs is required to stay competitive.
Pergamon
© 1998ElsevierScienceLtd. All rights reserved Printed in GreatBritain PIh S0360-8352(98)00018-7 0360-8352/98$19.00+ 0.00
AN INTEGRATED METHODOLOGY FOR SURFACE MOUNT PCB CONFIGURATION
Zhongkai Xu, Ken Carlson and Richard Kurschner
Sabah Randhawa
Board Build Operation Tektronix, Inc. Portland, Oregon 97077
Oregon State University Corvallis, Oregon 97331
and Man
r
Engmee
ABSTRACT An integrated methodology for surface mount printed circuit board assembly configuration is described. The methodology involves component-to-feeder assignment, feeder bay distribution among components, board family formation, and machine program generation. Applications result in significant reduction in setup times and in planning and scheduling times. © 1998 Elsevier Science Ltd. All rights reserved.
KEYWORDS Surface mount technology; PCB assembly; component allocation; placement sequencing.
INTRODUCTION The manufacturing of printed circuit boards (PCBs) is a major activity in virtually every segment of electronics manufacturing. The sequence of activities involved in PCB assembly include: • • • • • • • •
Receive board design and specifications from customers. Design component placement control programs, tooling, and fixture. Acquire raw PCBs and components. Schedule production of boards. Screen printed solder paste on to boards. Place surface mount components on boards. Reflow solder assembly. Place through-hole components and connectors. • Wave solder assembly. m Perform board testing. The focus of the research reported in this paper is directed at Surface Mount Technology (SMT) which is increasingly being used in the design and manufacture of PCBs. The placement of surface mount components is a key task in the assembly of PCBs. Surface mount equipment manufacturers generally design equipment for high speed operatiens. However, due to high mix of components and small batch sizes characteristics of many low-volume manufacturing environments, up to 70 percent of the production time can be spent on machine setups. Practices that minimize setups can significantly enhance system productivity. 53
23rd International Conference on Computers and Industrial Engineering
54
SURFACE MOUNT OPERATION At the start of a new production run, the appropriate assembly programs are loaded into a surface mount machine's controller. The PCB is transferred to a registered position and secured. The positioning system adjusts the pattern coordinates of the PCB. The placement head is then moved to the designed feeder location to pick a component. With the aid of a vision system the component is lead to the board site and the placement position is adjusted. The component is then placed on to the board. The pick and place process is repeated until all required components are inserted. The PCB is then released and transferred to another head or to the next assembly station. A typical pick and place machine has three control components: Process control, machine control, and supporting databases. The process control component retrieves the data needed for the placement process from the database in real time. It also checks if pre-placement activities are required, for example, presentation of new components. The machine control component is responsible for the control and monitoring of all activities associated with machine operation. This includes positioning of carriage with the required components and the operation of tape feed and tape cutters on the feeders. Finally, the databases store the information required during a placement cycle. This includes information about the machine, feeders, components, and placement programs. The decisions resulting l~omthe interactions among these three components can be divided into three levels:' •
Grouping-Selection of machine groups and part families and assignment of families to groups.
•
Allocation-Allocation of components to machines when a group has more than one machine.
•
Sequencing-arrangement of component feeders and sequencing of placement operations for each machine and PCB assembly.
Implementation of these decisions depend on the component technology and capability of the system, and product characteristics.
METHODOLOGY The objective of this research was to develop a systematic and practical methodology for machine feeder assignment decisionsto reduce machine setup times. A unique feature of this methodology is its integration o f c o ~ t - t o - f e e d e r allocation, feeder bay distribution for machine carriers, and automatic PCB program generation. The methodology consists of four major components: Component-to-feeder assignment, Fixed feeder bay allocation, board family formation, and machine program generation.
Component-to-Feeder Assimunents The first step in the placement process is installing of components into feeders. A feeder may have one or more tracks and each track can hold only one ~ t . Multiple feeders can hold one or more components of the same type, i.e., different types of components can not be mounted into the same feeder. Two small components, 8 mm for example, can be simultaneously mounted into a double feeder.
tMcGinnis, L.F., et al. (1992). Automatedprocess planning for printed circuit card assembly, liE Transactions, 24(4), 18-30.
23rd International Conference on Computers and Industrial Engineering
55
A common practice for component-to-feeder assignment is based on comixDmt-board usage. Two ~ may be nssismd to a donble feeder if tbey have a similar board usage. This method may place two comp(mm~ with same board usage into a double feeder, but the two congxm~ts may belong to two different board families, resulting in wasted feeder space and increased machine setup time. This methodology uses a similarity measure for each pair of oomponents. The similarity measure is based on a component-board incidence matrix that defines the set of componmts required for each board. The assignment of components to feeders is determined by formulating and solving a 0-1 integer programming problem, where the objective is to maximize the sum of component similarities.
Fixed Feeder Bav Determination Prior research has focused on arrangement of different machines into manufacturing cells and the selection of the component types to allocate to each machine on the basis of similar processing requirements to produce one or more families of PCBs. This implies that boards with similar components will have similar machine configurations or setups. However, this is not always the case. Generally, setup for a board is based on a pre-configured machine program and configuration file for that board. Before a new PCB is assembled, all cmgmnmts must be in the feeders on the preassigned feeder locations on the machine carrier. When a new PCB arrives at a machine, if the madfine does not have all the components needed for this PCB and/or the needed ccantxme~ are not in the preassigned locations on the carrier, a new setup of component feeders will be required. This methodology divides the machine carrier into three different feeder bays: fixed, semi-fixed, and configurable. Logically, commonlyused componentsshould be placed in the fixed feeder bay in order to minimize the machine setup time. In most cases, the componeats allocated to the fixed feeder bay will not be removed (hence, no feeder changeover is necessary in this area) unless additional feeder spaces are required from the fixed feeder bay for large PCBs. It is assumed that the machine carrier has enough capacity to hold all the components of any single PCB, but not the total number of components for all the boards (in a planning horizon). This implies that the fixed feeder bay cannot take all the feeder locations on the machine carrier. To determine the capacities of the three feeder bays, a cost-benefit analysis is used to determine the breakeven points between the three categories. The analysis explores the trade-off between the benefits of adding additional components, say to the fixed feeder bay, versus the costs of taking one or more components off the fixed feeder bay due to inadequate capacity outside this bay.
PCB Family Formation The result of the first two steps in this methodology is to create a master feeder setup for all PCB types in the fixed feeder bay. As a result of using this master feeder configuration for all the boards, generally no feeder changeover is needed within the fixed feeder bay. To further enhance similarity within the boards, the boards are further divided into famih'es to minimize setup within families. Board families are kept together during board sequencing in order to reduce both the machine setup time and simplify daily scheduling operations. Usually, a board family would contain a variety of board types requiring a large number of components. However, a board family shares many common component types. The cost-benefit analysis of the previous step and the board families in this step result in pattifiening of the machine carrier into: (1) Fixed feeder bay that holds most of the ~ ~ for all the PCB types; no feeder changeover is needed within the fixed feeder bay unless there is inadequate feeder capacity for large PCBs, (2) Semi-fixed feeder bay that holds conanen ~ within board families; the feeders are fixed within a board family but changeover is required between board families; and (3) Configurable feeder bay that holds the remaining components which cannot be placed into the fixed or semi-fixed feeder bays.
56
23rd International Conference on Computers and Industrial Engineering
PCB Machine Prot,ram Generation Once the fixed feeder bay is determined and the board fatuities are formed by the partitioning procedure described in the previous sections, the correspondlnS machine configuration and programs for each board are generatedthrough a machineprogram generator or optimizer. A master machine configuration is created based on the components allocated to the fixed feeder bay. This is followed by a group configuration file for each board family based on the ~ assismd to the semi-fixed feeder bay for that gronp. Finally, the machine configuration file for a board is generated from the group configuration files. The machine program generator, interfacingwith appropriate database, automatically generates these configuration files. This greatly speeds up and simplifies the machine program generation process and provides a repeatable procedure for PCB configuration that is responsive to a dynamically changing manufacturing environment.
CONCLUSIONS This methodology was applied to a large sample of industrial data involving thousands of components and hundred PCBs on two surface mount machine production fines. Machine carrier capacity of these lines was 300 feeders with each feeder capable of holdinga singlec o ~ t except for double feeders which can hold two 8 nun components. Comparison with a previously used spreadsheet-based tool showed a 60 percent increase in similarity value obtained in component-to-feeder assignment. After components were assigned to feeders, the machine configuration files were generated. Evaluation across all experimental conditions showed the proposed methodology to reduce the machine setup by approximately 15 percent. Actual production d~t~ gathered over several weeks is also consistent with the results of the simulation evaluation. Furthermore, by creating integrated computer modules for the methodology described above, the time to regeneratemachine programs for a new production line configuration is reduced from weeks to days. This is critical in today's manufacturing environment where the product mix is continuously changing and responsiveness to changing market needs is required to stay competitive.