|Covers|| Learning outcome 3
|Notional workload||30 hours|
|Comments||For information on submitting assignments, please refer to the AMI home page under Students, Assignments|
|Submission date||Midnight at the end of study week 8
Please refer to the module planning chart for the date
As described in the Module Descriptor, this module is assessed by three assignments, focusing successively on components and boards, on relevant ‘Design-for’ aspects for the board and assembly, and on making appropriate technology, materials and process choices at the system level. For Assignment 2, the challenge is to analyse design faults on a specific assembly, and make recommendations on DfF, DfA and DfT good practice and for reducing the incidence of faults.
We commissioned a ‘bad practice exemplar’ by asking Plexus to modify a good design (provided by Valor) to demonstrate the most likely kinds of faults in each of the areas Design for Fabrication, Design for Assembly and Design for Test. The board is a ‘fairly busy’ real design, and is representative of a typical board of the 2000 vintage, so it deliberately does not operate at the state-of-the-art boundaries. It has been screened by the CAD system, so there are no gross errors, but the check was done against an minimal set of rules such as those that might be applied by an uninformed user, leaving a number of issues for you to spot.
Your task is to identify and evaluate the problems, and suggest ways in which they might be put right. In doing this you will have to apply the course material to this deliberately incorrect design, using the many sets of guidelines found in it and during your own research. Where necessary, you will need to create a solution that will be the ‘least worst’ compromise between competing objectives.
You will also have to meet the demands of your partners: preferences vary between different fabricators and assembly shops, which is why every company publishes these, often on their web site. To provide a level playing field for everyone, we have provided sets of model rules for both fabrication and assembly. However, you may well find from your own research that some aspects of these rules are unduly restrictive, and wish to suggest negotiation with (or even changing) your company’s suppliers.
You first need to download:
In order to view the design, you must also install a Gerber viewer, if you do not already have one (see the notes in Assignment 1).
Having downloaded design and viewer, and familiarised yourself with the software, your task is to:
Bear in mind that the term “poor practice” has first to be interpreted in the light of the model rules, and not just your preferences, or the practices within your own company. However, as there is a requirement in all three assignments for you to demonstrate some research skills, providing evidence of reading and applying knowledge gained from outside the module, you are advised to search for other rule sets, and compare and contrast these. Your conclusions will inform the final part of your report.
We suggest that you tackle the element of the task in sequence, focusing in turn on particular likely problem areas and scanning the product for specific types of fault (but obviously keeping a note of any other faults you may stumble across!). Reflect on the way in which you structure your approach to each element of the task, as this will help you in the final section of the report.
1. Start by identifying as many as possible of the ways in which the exemplar does not represent best practice as regards Design for Fabrication, and evaluating what effect each specific example of poor practice would have on the quality, cost or performance of the board or assembly.
To create illustrations, you will probably need to capture selected areas of the screen and import them into Word. A number of suitable ‘screen grabbing’ programs are available, such as SnagIt, where a 30-day free trial version can be downloaded from http://www.techsmith.com/. However, the zero-cost way is to press <Print Screen> on your keyboard to capture whatever is on the screen at that time. To recall this image, open the Microsoft Paint program. This is installed with the Windows operating system, and usually has a short-cut located in Programs, Accessories. Then press <Ctrl-V> to paste the image into Paint, where it can be edited and manipulated and finally saved as a bitmap, gif or jpeg image.
There is a major ‘clanger’ with one of the Gerber files which tends to obscure other problems. You can make life much easier for yourself by emailing your tutor to ask for a corrected file, but note that you will only be sent this if you ask for the right file and your email correctly identifies the cause of the problem.
2. Then identify as many as possible of the ways in which the exemplar does not represent best practice as regards first Design for Assembly and then Design for Test, again evaluating what effect poor practice would have on the board or assembly.
You might have expected an assembly house to be given information in addition to the Gerbers supplied. If you can identify specific needs, please request these from your tutor by email – you might just get lucky!
3. When you have found most of the problems, suggest ways in which the board/assembly might be redesigned in order to overcome your criticisms. Putting the problem right may involve simple changes, or require a fundamentally different design approach.
4. Your recommendations from the three different perspectives (Design for Fabrication, Design for Assembly and Design for Test) may conflict, so you may need to create a solution that is the ‘least worst’ compromise between competing objectives. Consider and report on whether there are any areas where compromises would have to be reached in order to meet as many as possible of the criteria for optimum design.
5. Reflect on this exercise and draw some general conclusions as to how the company might approach the task of improving the quality of its designs and avoiding such poor designs in the future.
6. The task so far has concentrated on the board layout. Using the material from the module, and your other researches into what constitutes a manufacturable design, identify and comment upon other aspects of the product for which this board is intended that the company should take into account when “designing for excellence”. Where you don’t have sufficient detail on the product, identify what information you would need to collect in order to make an assessment. Where you choose to make any assumptions about the product, these should be both realistic and explicitly stated.
Compile a report summarising:
You should assume that the members of your audience are designers, who have some knowledge of the basic processes but do not have detailed understanding of the manufacturing requirements.
As a guide, you are unlikely to include all the points we expect to find if your main report has fewer than 1,200 words. There is no maximum word count as such, but excessive length will be penalised. For this assignment you will need to put your analysis and supporting material in appendices to the main report, in order to keep your script concise and well-argued, and its structure clear.
As always, you are strongly recommended to re-examine your draft report and conclusions to check that you have covered all the elements required in the report.
Bearing in mind that you will need to make reference to research findings in an appropriate and consistent way, we suggest that you use end-notes for references (leaving footnotes for incidental comments) and that you adopt one of the standard citation styles (see the links at http://www.lib.gla.ac.uk/researchskills/citationstyle.shtml for information). Also, given the transitory nature of some web sites, we recommend that you retain electronic copies of any material cited.
The maximum marks available for each element of the report are as shown in the table below:
|Identification and explanation of areas of poor practice||
|Suggestion for overall design improvements||
|Recommendations on approach to design improvement||
|Analysis of other aspects of “design for excellence”||
|Demonstration of research skills||
|Quality of presentation (including introduction and conclusions)||
For information on grades, please refer to the AMI home page under Students, Assignments, Marks and Grades.