The component placement process: challenges and considerations 101
The mounting process often utilises pick-and-place systems, which is still the most efficient way to mount components onto boards — but as components get smaller, this process becomes a constant battle to ensure the components are mounted accurately.
Focusing on some of the key challenges during the production of the printed circuit board, including the mounting process, we explore how to overcome some of the pain points, as well as potential difficulties that may occur in the future. Utilising this document to implement a proactive approach may help you to minimise some of these potential problems before they occur.
Miniaturisation of holes
As we discussed in the article ‘The screen printing process: challenges and considerations 101’, components are constantly decreasing in size, sometimes requiring an aperture size of 0.1 mm. When producing boards requiring apertures of 0.1 mm to accommodate the 0201 chip, it introduces challenges that need to be addressed from the outset such as increasing routine cleaning and inspection.
Cleaning: Needless to say, additional requirement to increase these mandatory processes costs valuable time. To minimise wasted production time, some manufacturers have introduced systems that are designed to provide a quick-release nozzle, using a jig. It can then be replaced with a clean nozzle, while the current part is cleaned in an ultrasonic cleaning system. This process can help to minimise downtime, while ensuring your system is kept clean from debris.
Nozzle health check: Checking the health of the nozzle is critical and this can be categorised into two parts — a visual check and a performance check.
- Visual check — This can prevent a build-up of debris before it occurs. Any debris on the nozzle, particularly at the tip, can impact the recognition of the components and potentially lead to mounting failure. Typically, if you maintain a good clean nozzle, it will ensure you maintain a good recognition rate. A visual check will also ensure the nozzle stays aligned. Any deviation can result in a decrease in pick-up rate, but potentially an increase in mounting failures too.
- Performance check — This includes the vacuum functionality and the spring action of the nozzle. Both of these actions are critical in maintaining good pick-up rate and mounting consistency, as well as accuracy. If there are any inhibiting factors preventing the nozzle from performing its full spring action, it can also lead to component breakage.
However, nozzles that are manufactured from ceramics with bespoke ESD coatings improve the stability and durability of the nozzle. This will also help prevent deformation from premature wear, which could lead to the nozzle sticking. The ESD coating will also ensure that the movement of the nozzle does not create a build-up of electrostatic discharge.
Performing both visual and performance checks are imperative, especially with 0201 components, which require high-precision throughout. This is especially the case during the pick-up process where the components are micro size.
Maintaining high-precision pick-up
Maintaining high-precision pick-up requires constant evaluation of several factors including pick-up position and height, as well as the vacuum level and the build-up of static charge from the tape.
- Pick-up position — Position of the pick-up needs to be accurate, but there are a few aspects that can cause pick-up to become displaced. These include elements such as the accuracy of the tape alignment, nozzle distortion and feeder plate positioning, as well as the actual alignment of the feeding by the feeder.
- Pick-up height — Clearly this has to be set up correctly at the start of the process, but there are other variables which can affect the accuracy of the pick-up height including the tolerance of the feeder head and the spring action of the nozzle itself.
Any abnormality in the spring action that inhibits a fluid motion can cause issues with the pick-up height.
Ensuring accuracy and working out any issues with a process of elimination can become tedious and very time-consuming. Some systems have been developed with functionality that enables engineers to teach the machine to maintain both pick-up height and positioning. This is achieved by ‘teaching’ the system to pick up at the centre of the nozzle every time, by recognising the image of the nozzle tip. It then automatically corrects any deviation off the centre.
Pick-up height can be taught by measuring the pick-up position and the height of the tape by contact tip with the nozzle. Comparison between the current setting can provide a different value. This can be input back into the system for increased accuracy, simultaneously minimising damage to component parts.
Optimising mounting onto the board
Assuming the pick-up height and the pick-up positioning are set correctly, the focus moves onto ensuring the components are mounted correctly onto the board.
One of the main considerations is mask thickness in relation to the component part size. For example, if you are intending to mount 0201 or 03015 components onto the board, you need to ensure you have set the mask thickness to between 40 and 60 µm.
However, as a component’s size increases it requires a thicker mask, so if the 0201 components are integrated onto the board with larger components (1005), this will require higher levels of mask thickness to account for the variation in the size of the components.
Another solution is to consider utilising solder paste in chip form. Recognising the increasing complexity of board designs, some suppliers now offer the paste in chip form so it can be placed on or next to the pads, where an increase in the amount of solder is required, ie, for the larger components on mixed boards.
Root cause failure analysis (RCFA)
Unfortunately, even if you ensure best practice has been implemented and you have done everything you can to ensure production of a good-quality PCB, you could still end up experiencing unexpected faults.
Cameras and vacuum sensors can inform you of issues such as tombstoning, or if the components aren’t released onto the board, but don’t provide any information as to why these issues have occurred.
Utilising a light high-resolution camera with a wide field of view, along with analysis software, could provide rapid analysis feedback, minimising downtime. The software can analyse each image to detect inaccuracies during the pick-and-place steps. However, it is essential that the system is configured accurately and synchronised to firstly capture the image and analyse it at the exact point of picking and placing.
Multi-Accuracy Compensation System (MACS)
The MACS system which has been introduced onto some of the Yamaha YS series mounters provides engineers with real-time machine vision. Utilising side-view and upward-looking cameras, the system can identify the centre of the component and, by capturing its position with the centre of the nozzle, it can automatically correct any deviation that occurs in real time.
Utilising the MACS system feature on the Yamaha YS series could reduce positional error from around 30 µm to less than 10. Find out more information on the Yamaha YS series here.
Taking everything above into consideration, we have listed the main considerations below, which can be utilised as a checklist. There is no winning formula, because every aspect from the design (including the mixture of component size) to the cleanliness of the nozzle needs to be considered.
Some factors can be counterbalanced with tools and functions on your equipment, such as the ‘teach’ mechanism, helping you to achieve the best results.
- Invest in an ultrasonic cleaner and a spare nozzle to maintain accuracy and efficiency.
- Conduct both a visual check and a performance check on the nozzle regularly.
- Invest in a quality nozzle with an ESD coating to prevent sticking and electrostatic discharge.
- Follow the steps to ensure both the pick-up position and the pick-up height are accurately calculated and maintained.
- Utilise ‘teach’ functionality to ensure accuracy and consistency.
- Investigate solder paste in chip form. This can be utilised by your pick-and-place machine, for boards designed with a range of component sizes.
- Minimise downtime by installing and configuring analysis software to provide feedback on why a failure has occurred.
- Consider upgrading your system to one of the Yamaha YS series mounters and benefit from MACS system functionality, reducing positional error to less than 10 µm.
Originally published here.
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