Posted on 24 Mar, 2016 by Richard Barratt
Fitting an incorrect component to a printed circuit board assembly (PCBA) is bad news. If an electronics manufacturing service (EMS) provider makes such a mistake they risk causing themselves costly rework or damaging the reputation of their customers.
Hopefully, the issue gets spotted at automated optical inspection (AOI) or during test - but what happens if it doesn’t? It’s probably best not to think about this too much for now.
Thankfully, there is a software solution available that has worked well for a number of EMS companies. The purpose of this blog post is to look at how one such solution, MYLabel from Mycronic, can save time and help minimise the chances of human error when setting up pick and place machines.
MYLabel is not a new piece of software. In fact, it has been around for many years but does offer a simple yet effective solution to EMS suppliers, regarding lowering the risk of placement error. To understand the benefits of using the software, I thought it would be useful to first explain the surface mount (SMT) set up process, both with and without it.
Without the use of this type of software
Step 1 - First of all, the EMS provider will want to "optimise" the build. If they use another software package called MYPlan, the engineering team will determine exactly how they want to approach the build. The parameters entered into the software at this point will determine how the pick and place machines react. Broadly speaking, there are two options. One reduces the number of feeder changes during the build, which is great for when multiple variants of a product are being produced or if shift staff levels are low. The other seeks to reduce overall assembly time, which is suitable when larger batches are being produced.
Step 2 - Once this process is complete, a pick list is generated, which highlights the feeder type and magazine each component needs assigning to. An operator then works through this list, ticking off each line as they go, until all electronic components are placed onto feeders and then located within magazines.
Step 3 - When the build is ready to be run, each magazine is slotted into the SMT machine by the operator. As far as the pick and place machines are concerned, all of the components needed for the build are now loaded and, crucially, in the right place. Unfortunately, this last step is also manual and relies entirely on the operator getting this right. The EMS supplier will often insist an additional check is in place here with another operator or "buddy" working back through the pick list and machine to ensure that all the magazines and feeders are loaded in the correct position.
Unfortunately, if any components have been placed in the wrong position the SMT equipment will still attempt to fit them. While in theory the machine will fail, some devices are not electrically tested prior to placement and could therefore still end up on the board.
Using MYLabel software
The first step above remains the same - i.e. the pick and place machines still need to be "optimised" for the works orders being built. A pick list is also required, showing the operator which feeders each component should be fitted to and where in the magazine they need to be placed.
The difference relates to the material the operator is presented with - specifically, the label information attached to the goods. Before machine set-up, incoming materials have a unique label applied to them. These labels can either be created at the time components arrive into the EMS supplier’s facility, or during the picking or "kitting" stage. This new label contains all the data taken from the original label but also contains a unique carrier ID.
An open format Microsoft Access database is used to store the part information, along with previous data from past jobs. For example, details of when a component was last used the angle of pick up, the feeder type and the step length - i.e. the pitch between the components.
When preparing the job, the operator works through the pick list to ensure all the components have been supplied. The MYPlan optimisation software produces a kit list and the operator then scans each carrier ID label and designated feeder. This process links the feeder to the component so that when the feeders are placed into magazines and into the machine they are recognised, regardless of position.
Clearly attention still needs giving to the kit list and feeder locations to ensure the build is optimised but the main problem of an incorrect part being loaded, picked and then placed is removed.
Software solutions such as MYLabel can help EMS providers reduce the possibility of fitting incorrect parts during the SMT stage. They also remove the need for additional checks to be carried out by other members of the team which obviously add extra time and cost to the overall process. If you are unsure what lengths your EMS provider goes to in reducing placement errors, why not arrange a visit or site audit to find out.
Image by Paulo
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