Page 56
www.us-tech.com
March, 2012
Assembly and Packaging
Prototype Quality : Getting More Than You Pay For
By Nolan Johnson, CAD/EDA Manager, Sunstone Circuits T
he prototype fabrication pro - cess is of critical importance in catching design errors early
and effectively. It is the prototype hardware, after all, which verifies the original design intent embodied by the CAD file contents; the rela- tionship is symbiotic. When a design team puts their first prototype onto the workbench for testing and verifi- cation, the team must simultaneous- ly debug the following:
l The concepts in the schematic design.
l The layout’s implementation of the concepts.
l The behavior of any firmware/ software onboard.
l The ability of the chosen parts to interact as expected from the component datasheet documentation, functional specifications, and schematic- driven simulation data.
l The fabricator’s ability to manufacture what the layout instructed them to build.
That’s a lot to debug, all at the
same time. The more a manufacturing provider can shorten this list for the design team, the better. And this is where the manufacturer’s quality rates become a key method for meas- uring your prototype provider?s over- all contribution to your design cycles. The more the board fabricators can remove debugging discussions that start with “I found a short in the board you built me,” then the more the board manufacturer can help the design team target functional behaviors, instead of build errors. And that results in a shortening of the product design cycle in other meaningful ways.
Optimization for Production In optimization for production,
plenty of attention is paid to design issues that may reduce the overall manufacturing yield of the end prod- uct. Production, after all, is a world where shaving pennies on 10,000 units a month can make the differ- ence between profits and losses for some products. A design that results in 98 percent yield during manufac- ture is going to be much more com- petitive (price, reliability, market reputation for quality, durability, etc.) than a comparable product with
a 75 percent yield. The wisdom is that, if the board has a low yield just getting out of the factory, that board is going to be fragile in the field, too. Designing for yield is also helping the cause of designing for durability. The idea is the same during pro-
totype — design for yield — but with different target criteria: l Production designs optimize for volume production.
l Accessibility. l Yield.
Schedule Adherence In a revealing comparison, UPS
delivers a nationwide 91 percent on- time delivery for domestic next-day 10:30am service. Sunstone Circuits’ actual on-
time delivery rate: 99+ percent. Competitor #1 published on-time
1,000 orders per day, the difference between 95 percent and 99 percent annualizes to over 11,000 additional late shipments per year. This is a very different way to look at the data. That delta in on-time shipments causes project delays for over 11,000 design teams, on 11,000 different time-critical projects. Whether a late shipment strikes your design or not, that’s still a whole lot of industry- wide R&D time lost to manufacturer late shipments. Let’s monetize this, so as to put
Minimizing engineering changes early in the prototype process leads to higher yields during production.
l Prototypes optimize for quick turns.
l Production optimizes component costs.
l Prototypes optimize functional verification.
l Production designs work to reduce manufacturing costs.
l Prototypes work to reduce design errors.
Manufacturing quality has a
decided impact on prototyping and small-run board Return on Investment (ROI.) A Printed Circuit Board manufacturing process can greatly affect both individual design teams and the industry as a whole. Manufacturing quality can be
categorized as:
l Schedule Adherence (on-time delivery).
l Design Adherence.
delivery rate: 98+ percent. Compet - itor #2 published on-time delivery rate: 95+ percent Other industry leaders in the
prototype PCB space promote their 95 percent on-time delivery rate. All three deliver on-time rates that exceed that of UPS. The difference between 95 percent and 99+ percent seems relatively marginal, at least in the small quantities associated with a single order.
l 95.0 percent of 1,000 = 50 late shipments
l 99+ percent of 1,000 = 5 late shipments
Hard-to-Get Data Exact shipment information
from the top three prototype PCB manufacturers is difficult to locate. That said, if a quickturn prototype manufacturer ships an average of
it in perspective. Let’s assume that a late shipment results in $1,000 in additional expense to the customer design team. This value seems high for some projects, but could easily be low for many others. Given this assumption, then, a manufacturer with a 95 percent on-time rate, and 50 late shipments daily, is responsi- ble for $50,000 in additional cus- tomer cost at 50 separate customers, daily. That’s an excess of $12M/year in wasted customer budgets. In con- trast, a 99+ percent on-time perform- ance causes between $1M/year and $2M/year in customer inconvenience. Thinking of it in these terms, even $1M seems excessive. That’s why Sunstone Circuits continues work to improve on the current 99+ percent on-time performance. The general consensus among
prototyping engineers is that spins equal progress. Some engineers mis- interpret this as meaning that more spins are beneficial. Instead, the objective is to spin regularly, but to maximize the forward progress
Design adherence is the ability of the manufacturer to build exactly the board that the designer created.
between spins. This will result in fewer spins overall, a shortened proto- type design phase overall, and a more cost-effective development project. Design Adherence is the ability
of the manufacturer to build exactly the board that the designer created. We’re removing issues in the imple- mentation of the circuit from this dis- cussion, and focusing instead on the axiom that the layout file as submit- ted is the gold standard. Did the
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