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.
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:
• a chip ceramic capacitor
• a chip resistor or resistor network
• two other types of passive component with different constructions
• a mechanical component
• an integrated circuit.
Using information from the manufacturer and from the module material, write a brief description of each component, covering:
• the materials used
• the processes involved in making the part
• the mechanical characteristics of the component
• any assembly, handling, reliability or other application issues associated with this type of device.
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.
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 interconnection demands of the circuit currently require four signal layers and two internal power/ground planes
• there are no high currents (based on the maximum ratings of the components)
• there will be some restrictions on layout to accommodate signal integrity good practice, but no requirement for controlled impedance traces.
The manufacturing team have also told us that:
• whilst the product is to be manufactured in volume, there are a number of variants both to board layout and component population
• it is most economic to buy boards in large batches, corresponding to 2-3 months usage
• not surprisingly, the team is under pressure to reduce costs!
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.
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:
• double-sided reflow assembly, with through-hole components replaced as far as possible by surface-mount parts
• more integration of the silicon circuitry, and the use of TSSOP and micro-BGA parts
• a more complex (though much smaller) board with six signal layers, finer traces, and probably some via-in-pad connections.
Briefly outline to the procurement team the implications of this change as regards both components and board.
The essential elements you will need to access (from the links given) are:
• the pair of Gerber files that describe aspects of the board
• the bill of materials spreadsheet (this is locked, so accept the option to open as read-only)
• the views of the component side and underside of the circuit (two .jpg files, each 1.12MB)
Your submission should be a report to the procurement team within your organisation covering the following elements:
• a critical evaluation of the components used
• recommendations for board materials
• an evaluation of fabrication processes
• the implications of possible future changes.
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.