Design for Product Build

Assignment 1

Covers Learning outcomes 1 & 2
Units 1–4
Notional workload 25 hours
Weighting 30%
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 4
Please refer to the module planning chart for the date

Introduction

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. In Assignment 1, we are starting with the parts from which assemblies are made, and asking you to investigate the components used, the properties of the board materials, and the fabrication issues that relate to a representative assembly. The aims of this assignment are that, in line with the needs of the real world of work, you will learn:

In order to make the task as realistic as possible, and create a level playing field for everybody, this assignment is based on the real product shown in Figure 1, made for Pace Micro Technology at Solectron's Dunfermline factory. We are most grateful to both companies1 for permission to adapt their work for training purposes. We wish to emphasise that, although the facts given about the components and layout are accurate as they relate to a particular version of the product, other aspects such as the board specification represent normal practice and are not based on the actual design requirements. In particular, scenario elements (any “What if . . . ?”s), whilst realistic, come solely from our imagination, and bear no intentional relationship to the views or strategy of either company.

1 Pace Micro Technology plc (http://www.pacemicro.com/corporate/home/main.asp) is a market leader in the design and sale of commercial TV set-top boxes. Solectron (http://www.solectron.com/index.html) is a major provider of electronics manufacturing services based in Milpitas, with 57,000 employees and global facilities and support.

Figure 1: External view of a typical ‘Foxtel’ set-top box and its internal construction

External view of a typical ‘Foxtel’ set-top box and its internal construction

 

If you have studied AMI4982 Lead-free Implementation, you will be familiar with the product, and know that it was converted to lead-free during the first half of 2004. For the purposes of this assignment, however, you should assume that the transition has now been made, and that the design is being made in volume using RoHS-compliant materials and components.

Most of the information that you need to tackle this assignment may be found in Units 1–4 of the course text, but 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. Remember, however, that it is much more important and relevant to your studies to integrate the materials you import into a coherent argument than it is to collect pages of URLs. Also, you are advised to keep external referencing under control, or the volume of material available will overwhelm you!

The task

The first three elements of the task are:

  1. To critically examine a selection of the components used on this design
  2. To recommend materials to be used in making the board for this design
  3. To identify the processes involved in fabrication, and describe how these create a reliable conforming board.

The target audience for your report is the procurement team within your organisation, who have asked for background information on component technologies and need a better understanding of the issues surrounding board specifications.

However, because you are privy to the company’s latest developments, you decide that it would be prudent to scope for your colleagues the changes that might be needed in consequence of these plans. So the final element of the task is to reflect on the changes to components, materials and processes that would be involved in a significant reworking of the product.

The components

Links to the information available on the design are given below in the section on Resources. By combining the bill of materials with the physical view of the product and the Gerber information, you should be able to identify most of the components on the board. [Particularly if you do not have everyday exposure to electronic assemblies it will help you to take a good look at the assembly and check that you know the function and construction of all the parts.]

To make this easier, the images are high definition, and it may be useful to use a graphics viewer that will give you an enlarged picture. The Windows Picture and Fax Viewer (right click in My Computer and ‘Open With’) is better than the default Windows Media Player, but tools that allow you to grab hold of the image to steer it around, such as Adobe Photoshop and ACDSee (ACD Systems), may be more convenient.

The first sheet on the bill of materials is an “as it came” list which is identical to that originally provided, except that the part numbers have been simplified. The description on the bill of materials falls short of what one would wish in a number of ways:

This is not untypical of a real life situation for a contract manufacturer!

1 OEMs would normally have an Approved Vendors List (AVL), but freedom to procure is often an advantage to a contract manufacturer.

2 When trying to identify a particular component, you need to be creative in reviewing the description. Start with the full part description, and look for recognisable fragments, as in SMDIC-MAX214CWIRS232TRANSCEIVER, made up from

SMDIC short-form for the type of device
MAX214 manufacturer’s base part number
CWI a package designator, or packaging details, or both
RS232 transceiver circuit function

A search for MAX214 makes it quite easy to identify the manufacturer of this part as Maxim. In some cases, looking at the photograph may also help.

3 Bear in mind that this board is used for a number of variants, so some parts are deliberately omitted, and other locations are associated with multiple part numbers.

On the second .xls worksheet, we have divided the list of component into generic types, and also indicated the package styles for the active components. The components fall into a number of representative groups:

Through-hole components   SM components
Passive components   Passive components Discrete active components
Disc ceramic capacitors   Chip ceramic capacitors Diode, small outline
Electrolytic capacitors   Chip resistors Transistor, small outline
Inductors and transformers   Resistor networks  
Thermistors   Inductors and transformers  
Varistor      
Specialised components Integrated circuits and assemblies
Fuse   Ferrite beads Small outline active devices
Gas plasma arrester   Crystals ICs, QFP and gull wing
Mechanical components ICs, leadless arrays
Card reader   Metalwork  
Connectors      

Ideally, we would like you to have a working knowledge of the materials, construction and reliability issues relating to the components in all these groups! To make the task practicable, we want you to select one specific component in each of the following categories:

Using information from the manufacturer and from the module material, write a brief description of each component, covering:

We have deliberately allowed you some choice in which components to select for evaluation so that your report may reflect to the procurement team your understanding of the very wide range of technologies used in components and the variety of potential application issues.

The board

For reasons of commercial sensitivity, and also to simplify the information, there is no board specification, and the pair of Gerber files contains only information related to the top (visible) layers of the board. However, we are able to get a clear picture of the level of interconnection density involved (which is only modest). Also, we know that the assembly is mixed technology, and that chip components on the underside of the circuit are glued before the joints are made by wave soldering.

For the second and third parts of the task,you may assume for the board layout that:

The manufacturing team have also told us that:

What we now need to select is an appropriate combination of laminate, foil and board finish. For this part of the task, research the alternatives, and justify your recommended specification. In doing this, you may have to explain some of the issues and trade-offs, and should consider presenting such information in tabular form.

Board fabrication

Having chosen the materials, all you have to do is get the board made! For this third part of the task, give an overview of the work that would be carried out by a board fabricator making this design, covering the process sequence and the individual processes, but concentrating on the ways in which manufacture would be controlled and quality assured. Bearing in mind your audience, you should also identify any options for reducing costs, other than buying more boards or pressurising the vendor!

What if . . .

One of the marketing team has suggested a totally different use for the product, for which its size would need to be drastically reduced. The engineering team have suggested a reworking of the circuit that uses:

Briefly outline to the procurement team the implications of this change as regards both components and board.

Resources

The essential elements you will need to access (from the links given) are:

Recommendation

Rather than use the files on-screen, download them by right-clicking on the link and choosing “Save Target As”.

 

In order to view the Gerber files, you will also need a Gerber viewer, and this is worth experimenting with now, because it will be needed again for Assignment 2. Designers already using a CAD package will probably have this facility, and are recommended to use whatever software they are familiar with – in this module, struggling with software is not part of the learning experience!

If you don’t have a Gerber viewer, a number of programs are available for free download upon registration. All of these offer broadly comparable facilities, so it is up to you to decide which to use. Names you will come across most frequently are GC-Prevue from GraphiCode (http://www.graphicode.com/) and ViewMate from Pentalogix (http://www.pentalogix.com/), but there are other suitable packages. For reasons of time economy, we selected GC-Prevue as the one for which we would write step-by-step instructions supporting its use for this module: read our Guide to using Graphicode GC-Prevue for information on installation (11.1MB zip file download) and operation.

if you have problems in accessing these resources, because of the slow speed of your internet connection, or because you operate within a firewall, please contact your tutor to request the files on CD.

Requirement

Your submission should be a report to the procurement team within your organisation covering the following elements:

You can assume that the members of your audience have a general awareness of components and boards, but this is from a procurement perspective, and they have little detailed knowledge of “what's in the tin”, and the implications of component and board technologies and specifications for their manufacturing colleagues.

As a guide, you are unlikely to include all the points we expect to find if your main report has fewer than 2,000 words. There is no maximum word count as such, but excessive length may be penalised.

In order to keep your script concise and well-argued, and its structure clear, you may find it helpful to provide relevant supporting material in appendices to the main report.

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!

Caution

It is very easy to get intimidated by the apparent complexity of assignments like this. Just remember that this is just a scenario, intended to be like real life, and enter into the spirit of it! Approach your report-writing with the questions: What is that these guys need to know? How can I give them a flavour of complex issues without overwhelming them with detail?

We strongly recommend creating the framework first, only then collecting the meat of the report.

 

Marking scheme

The maximum marks available for each element of the report are as shown in the table below:

Element
Maximum marks
Critical evaluation of the components used
35%
Recommendations for board materials
20%
Evaluation of board fabrication
15%
Implications of possible future change
10%
Demonstration of research skills
10%
Quality of presentation (including introduction and conclusions)
10%

For information on grades, please refer to the AMI home page under Students, Assignments, Marks and Grades.

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