PROCESS IMPROVEMENT |
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An Increase in Efficiency and Productivity
It’s a shocking statistic to read that within the electronics industry many surface mount operations, particularly within the sub-contract manufacturing sector, run as low as 20% efficient.
There are many reasons that contribute to this figure but it fundamentally means that only 20% of the capital investment is being utilized. Financially speaking, this will lead to a higher cost of ownership and a slower return on investment. For the customer, it can cause longer lead times for their product and therefore the business will not be as competitive in the market place.
With production efficiencies at this level there will be many knock-on effects that will have an impact on the business such as larger batch sizes, more parts in stock, more assemblies in WIP (work in progress) and slower reaction times to customer change requirements.
With all this in mind there is a strong incentive to improve efficiency while maintaining quality.
There are many reasons that contribute to this figure but it fundamentally means that only 20% of the capital investment is being utilized. Financially speaking, this will lead to a higher cost of ownership and a slower return on investment. For the customer, it can cause longer lead times for their product and therefore the business will not be as competitive in the market place.
With production efficiencies at this level there will be many knock-on effects that will have an impact on the business such as larger batch sizes, more parts in stock, more assemblies in WIP (work in progress) and slower reaction times to customer change requirements.
With all this in mind there is a strong incentive to improve efficiency while maintaining quality.
Overall Equipment Effectiveness
There are many ways to improve the OEE (Overall Equipment Effectiveness) of the process that fall into three main categories – Availability (no stop time), Performance (as fast as possible) and Quality (no defects). By measuring the OEE it will be possible to identify the losses within the process and so develop ways to make improvements by eliminating waste.
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Availability – This takes into account the planned and unplanned stoppages. An availability score of 100% means the process is always running during the planned production time.
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Performance – This takes into account the balance of the process. A performance score of 100% means the process is perfectly balanced and is running without any small stops or delays.
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Quality – This takes into account the defect rate. A quality score of 100% means all work produced is free from defects with no rework required.
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Overall Equipment Effectiveness – The OEE takes into account all losses within the process. An OEE score of 100% means the process is running without any stoppages, in the fastest possible time and all work produced is completely free of defects.
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Machine Changeover - SMED
For most electronics assembly companies, contract electronic manufacturers in particular, machine changeovers will be one of the main causes for downtime. CEM’s will tend to have many customers and have a ‘high mix, low volume’ range of assemblies to build requiring many changeovers to be carried out.
Some companies have machine changeovers that take hours instead of minutes and with high hourly rates for machine time, there is a high incentive to reduce the changeover time as much as possible.
One commonly used term within 'Lean Manufacturing' is SMED - 'Single-Minute Exchange of Dies'. SMED is a system to reduce the time taken during equipment changeovers.
The definition of the machine changeover should also be understood as there are many activities taking place to maintain quality. For the purpose of this analysis the changeover will be defined as the time taken from the last conforming assembly of batch A to the first conforming assembly of batch B.
Causes for long machine changeovers are not always obvious and it is important to fully measure and analyse the current process before making changes to ensure the changes made will have the most process improvement without impacting on quality.
Process Summary
The surface mount production line is made up of a number of machines and each plays a particular part in the overall assembly process.
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- PCB Loader - Loads PCB's one at a time into the printer from a magazine at the start of the line
- Solder Paste Printer - Prints the solder paste onto the PCB's through a stencil
- Solder Paste Inspection (SPI) - Automatically inspects the printed PCB for solder paste defects
- Component Placement Machines - Places the surface mount components onto the PCB
- Pre-Reflow AOI - Automatically inspects the assembled PCB for missing or misplaced parts
- Reflow Oven - Assembled PCB travels through the heated zones to form the solder joints
- Post-Reflow AOI - Automatically inspects the soldered PCB for assembly defects
- PCB Unloader - Unloads PCB's one at a time into magazines at the end of the line
Measure Phase Observations
After the current state measurement has been completed it can be surprising to the see the observations made. Quite often there will be a significant difference with the total changeover time recorded between one line operator and another. This will depend on a number of factors such as:-
To address the above it is important to fully document the process and ensure all members of staff are trained to understand what has to be done. Standardise the process where possible, clearly identify any equipment needed and have defined storage locations when not in use. Regular meetings are recommended to encourage a strong team working environment and suggestions from team members to improve the process where possible.
- Process documentation
- Process and equipment standardisation
- Equipment identification and location
- Operator skill level
- Operator temperament
To address the above it is important to fully document the process and ensure all members of staff are trained to understand what has to be done. Standardise the process where possible, clearly identify any equipment needed and have defined storage locations when not in use. Regular meetings are recommended to encourage a strong team working environment and suggestions from team members to improve the process where possible.
Waste Walk - Quick Wins
An activity to carry out after the measure phase is complete is a 'Waste Walk' to identify 'Quick Wins' within the current process. Many of the points identified will be fairly simple with minimal cost to correct such as:-
- Shadow boards and labelled storage locations for required tooling
- Clearly labelled storage locations for solder paste, squeegees and consumables
- Part number consumables needed and ensure stock always available
- Feeder identification labels to detail what is loaded to the trolley and if ready for production
- Designated areas for trollies/feeders ready for changeover
- Quick belt-adjust PCB magazines that do not need tooling to adjust width
- Trolley kitting area to be organised and maintained using 5S
- Damaged feeders identified and ideally repaired or at least quarantined
- Location for component placement nozzles close to placement machines
Organisational Improvement
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One of the simplest improvements to implement is to appoint at least one member of the team to be a 'Changeover Specialist'. What this simply means is that when a changeover occurs that there is at least one person who is responsible for carrying out the required tasks needed to complete the changeover.
There are many companies that rely on the line operator to carry out changeovers and comparing this to a pit stop would mean the driver getting out of the car to change the wheels and refuel the car.
Internal and External Activities
The next step of the improvement process is to analyse the current changeover and identify which activities can be classified as 'Internal' and which are 'External' - Convert (where possible) internal activities to external.
Internal activities are those that can only be performed when the current process is stopped, while external activities can be done while the current batch is being produced, or once the next batch has started. An example of an internal activity is fitting feeder trollies and an external activity is collecting the necessary tools to carry out the changeover.
Internal activities are those that can only be performed when the current process is stopped, while external activities can be done while the current batch is being produced, or once the next batch has started. An example of an internal activity is fitting feeder trollies and an external activity is collecting the necessary tools to carry out the changeover.
Streamline Activites
Hopefully a number of internal activities will have been converted to external leaving a revised list of internal activities. All these activities should then be put into a 'Pareto Chart' to identify which activities take the most time and which take the least.
Every company will have different results depending on a number of factors such as the configuration of the line and type of assemblies being processed. Generally the parts of the process that take the longest during a changeover are the setup of the placement machines and 'First Article Inspection' as most activities relating to the solder paste printer can be external.
The setup of the placement machine(s) will consist of a number activities and one of the most important is setup of the PCB supports to ensure accurate placement of components. There are a number of systems available that are automatic and quick to setup but they can be expensive. If the assemblies being processed are single sided then more cost effective solutions are available - an example of which can be seen here.
First Article Inspection (FAI) can also be a common cause for delay during a changeover as it can be time consuming to verify the first assembly built is correct to the customer documentation. Component values can be a common cause for error due to an incorrect part being bought or loaded to the machine and so many machine manufacturers offer an option to fit 'electrical test' to verify parts picked are the correct value before placement.
If an automatic optical inspection (AOI) machine is available within the company it can be a quick solution to use this to verify the first assembly built but care needs to be taken to be sure the AOI program is correct and that it checks for all possible errors.
Every company will have different results depending on a number of factors such as the configuration of the line and type of assemblies being processed. Generally the parts of the process that take the longest during a changeover are the setup of the placement machines and 'First Article Inspection' as most activities relating to the solder paste printer can be external.
The setup of the placement machine(s) will consist of a number activities and one of the most important is setup of the PCB supports to ensure accurate placement of components. There are a number of systems available that are automatic and quick to setup but they can be expensive. If the assemblies being processed are single sided then more cost effective solutions are available - an example of which can be seen here.
First Article Inspection (FAI) can also be a common cause for delay during a changeover as it can be time consuming to verify the first assembly built is correct to the customer documentation. Component values can be a common cause for error due to an incorrect part being bought or loaded to the machine and so many machine manufacturers offer an option to fit 'electrical test' to verify parts picked are the correct value before placement.
If an automatic optical inspection (AOI) machine is available within the company it can be a quick solution to use this to verify the first assembly built but care needs to be taken to be sure the AOI program is correct and that it checks for all possible errors.
Process Documentation and Training
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Once all the improvements have been made and new changeover process created, it is of great importance to fully document, monitor, create visual aids and train all members of staff involved. So many process improvements are not as effective as they could be simply by the operators carrying out the tasks not being fully involved or aware of what is expected of them. It is also worth carrying out this process analysis and improvement on a regular basis as the company and customers change.
Double Sided Process Improvement
When assembling PCB’s with components on both sides a significant delay to the process is when switching from the first side to the second even if all components for both sides are loaded to the machine as a family setup.
This is mainly due to PCB tooling change such stencils and PCB support but there are also program changes such as placement, SPI and AOI.
This can be frustrating when running high volumes of an assembly as quite often all of the first sides will be assembled before starting on the second side and so it can be quite some time before a completed double sided assembly is available.
For double sided assemblies where both sides have components that do not exceed the limit set here, one solution to this challenge is as follows:-
Take an example PCB such as the one below
Side A
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Side B
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Due to this being a small PCB it would be designed into a panel containing multiple circuits usually all facing the same way so that all the ‘Side A’s are on one side and the ‘Side B’s on the other.
The proposed solution is to panelise with half of the panel containing Side A and the other half containing Side B being careful to position the panel fiducial marks in such a way that when the panel is flipped over it is identical - see below
The proposed solution is to panelise with half of the panel containing Side A and the other half containing Side B being careful to position the panel fiducial marks in such a way that when the panel is flipped over it is identical - see below
Doing this will enable one complete panel to be assembled needing only one stencil, one program for each machine and one first article verification. At any point during the production build the panels with one side being assembled can be put back through the assembly process without any change to the setup.
Design for Manufacture and Assembly
Many electronic assemblies are primarily designed based upon the function of the circuit, which of course is very important, but it is also important to consider the way in which the assembly is to be manufactured.
Manufacturing cost is a key factor to any electronic assembly and two of the main elements of the manufacturing cost are the labour cost (time to manufacture) and tooling cost such as solder paste stencils.
These costs can be a significant percentage of the overall cost and so anything that can be done to reduce them should be considered. If the assembly has components on both sides of the PCB one of the main questions to ask is ‘Can the assembly be designed having components on one side of the PCB only?’ If the answer is yes then this can be a significant cost saving as both labour and tooling cost will be reduced.
Manufacturing cost is a key factor to any electronic assembly and two of the main elements of the manufacturing cost are the labour cost (time to manufacture) and tooling cost such as solder paste stencils.
These costs can be a significant percentage of the overall cost and so anything that can be done to reduce them should be considered. If the assembly has components on both sides of the PCB one of the main questions to ask is ‘Can the assembly be designed having components on one side of the PCB only?’ If the answer is yes then this can be a significant cost saving as both labour and tooling cost will be reduced.