Evaluate manufacturing

Blog post: 2023-12-02-pcba-analyses

For the VDS

Can you tell me what the likely manufacturing volume is for this design? Was it optimized for a particular manufacturing volume?

The schematic itself does not indicate the intended manufacturing volumes or optimization specifically for volume. However, we can make some educated guesses based on the type of product and technology used:

For context, this is an automotive display system design over 12 years old.

Some likely volume assumptions:

• This is unlikely to be for a high-volume mainstream vehicle model. More likely a luxury or low/medium volume car.
• An annual production volume in the tens of thousands of units per year is reasonable. Perhaps between 10,000 to 100,000 units maximum per year.
• It’s unlikely this was optimized for volumes above a few hundred thousand per year based on the electronics and display technology used.
• Component selections lean toward reliability and capability over lowest cost, supporting lower volumes.

As for manufacturing optimization:

• There has likely been some optimization for automotive grade reliability, testing, qualification etc which adds cost.
• The redundancy in memory chips and connectors may indicate modularity/serviceability to support longer product lifetime was valued.

So in summary, while the exact volumes are unclear, this was likely aimed at annual production volumes in the 10-100k unit range based on capability and cost structure. It does not seem fully optimized for highest volume production lines above a few hundred thousand units per year. And some cost added to improve field reliability and serviceability over 10+ year vehicle lifespan.

Let me know if any part of this analysis seems unreasonable for the product!

Estimate the cost of the PCB and the cost of the assembled PCB assembly including identifying parts costs and assembly costs.

Unfortunately I do not have enough detailed information to provide highly accurate cost estimates for the printed circuit board (PCB) and assembled board. However, based on the era of design, technology used, and volume assumptions, here is an approximate estimate:

PCB Cost

• 4-6 layer board
• Assuming dimensions around 4 x 5 inches
• With volume in 10,000s per year
• Bare board cost likely $10 - $15 each

Component Cost

• Processor, memory, power ICs likely $15
• Display interface, op amps, discretes $10
• Passives, connectors - around $5
• Total Components ~$30 per board

Assembly Cost

• Assuming automation for volume but moderate complexity
• Likely 1 hour of labor @ $40/hr (typical blended rate)
• Add $2-$3 for paste, packaging etc.

Total Estimate:

• PCB: $12
• Components: $30
• Assembly: $42 —————- $84

Of course without complete requirements and volume specifics it is hard to get highly precise. But hopefully this provides some reasonable approximations of cost elements for a product like this! Let me know if you need any clarification or have additional factors I should consider in the estimate.

Any guess on how many layers are in the PCBs?

Based on the complexity of the schematic and the various functions shown in this automotive display system design, I would estimate that the main circuit boards likely utilize 4-6 copper layers. Some analysis behind this guess:

• A relatively high pin count BGA processor and multiple large FFC connectors indicate need for layer routing density.
• Partitioning of functionality across several boards implies a deeper layout is achievable rather than fewer single sided boards.
• The use of multi-layer boards to control noise, EMI and distribute power mentioned in prior analysis reinforces that assumption.
• Typical high reliability automotive designs seen today often leverage 4-8 layers to meet requirements and optimize performance.
• However, 12+ years ago when this was originally done, capabilities may have been more limited on layer count before higher counts became more cost achievable.

So based on those points, 4 copper layers would be reasonable minimum expectation to route the various functions cleanly. 6 layers provides even better separation for noise control. And anything above 6 may be overkill based on the components used.

Of course without the actual board files or knowledge of the specific PCB fabricator capabilities at the time, it’s difficult to conclude definitively - but estimated range of 4-6 layers is a reasonable assumption for this vintage automotive display system. Please let me know if I should reconsider or revisit any part of this analysis!

What features for development or manufacture can you identify?

Reviewing the schematic, I can identify several features that likely supported the design and manufacturing process:

Development/Debugging Support

• JTAG debugging interface for processor programming/debugging
• Test points provided for key signals to enable hardware debugging
• 0-Ohm resistor jumpers for certain signal paths or supply rails to enable modifications
• Pushbuttons likely used to trigger reset or functions during development
• LED indicators to provide power and status feedback

Manufacturability

• Many common passive components values used repeatedly for part reduction
• Some groups of resistors/caps standardized into single repeated building blocks
• Fine pitch QFN and BGA used to conserve PCB area
• Flat flexible cabling minimizes wiring bulk
• Similar functional groups partitioned by schematic page to simplify routing

Test/Calibration

• MCU and peripheral ports brought out to headers/connectors to facilitate testing
• Communication buses available through external connectors
• Analog filter networks allow tuning component values

These types of choices help reduce development time, enhance debugging access, improve manufacturability through consistency, and provide hooks to support production line testing. The end result is likely reduced cost and risk while preserving flexibility as needed on a lower volume product.

What can you say about testing time and costs?

Making reasonable assumptions on the verification approach for this automotive system, here is an approximate estimate for testing time and costs:

Testing Scope

• Functionality validation
• Environmental stress screening
• Standards compliance
• Reliability life testing
• Safety critical fault injection

Test Development

• Define test cases and equipment - 2 weeks effort
• Develop automated test scripts - 3 weeks effort
• Lab technician time - 5 weeks

Per Unit Testing Costs

• Functional test 20 minutes → $20
• Temperature Cycle test 2 hours → $40
• Vibration and EMI scans - 1 hour → $25
• Fault injection 30 minutes → $15

Total Estimate:

NRE Test Development - $15,000 Unit Testing Costs - ~$100 per system

Note lifetime reliability testing costs would be additional with investment in test sample pool.

Assumptions:

• Leverage some existing frameworks
• Partial automation balanced with manual debugging stations

Let me know if any part of this high-level test estimation seems inaccurate! Providing test cost guidance early helps validate budgetary plans.

Identify possible manufacturing test procedure and time

Here is one possible high-level test procedure for the manufacturing line along with estimated test times:

Incoming Inspection (30 mins)

• Visual check of boards and critical components
• Confirm markings, revision

JTAG/Boundary Test (5 minutes)

• Validate processor connectivity
• Program and test diagnostic code

Continuity Test (2 minutes)

• Automatic optical inspection of solder joints
• Check for electrical shorts

Power On Test (8 minutes)

• Apply input voltages, confirm power rail continuity
• Initialize system, confirm supplies within tolerance

LCD Display Calibration (5 mins)

• Screen luminance, grayscale, uniformity measurements

Integrated Functional Test (30 mins)

• Automatic execution of system level diagnostic suite
• Stimulate sensor inputs with fault injection

Final Audit (10 minutes)

Sample audits of completed units prior to shipment Total time: ~1.5hrs

Let me know if you would suggest refinements to this generic high-level test methodology and timeline for an automotive display product! Time on station directly influences cost and capacity.