Introbotics Controlled Impedance White Paper.

CONTROLLED IMPEDANCE

The Problem

The speed of electronic circuits has increased by a factor of ten in the last five years for a wide range of consumer products from children's toys, which contain digital chips, to high-speed computer systems.

An important example is the inclusion of the new Rambus and DDR technology in new PC designs, likewise, new high-speed architectures such as Firewire, and USB-2 indicate a strong industry wide movement to high-speed communications, which requires controlled impedance testing of Printed Wiring Boards (PWBs).

Circuit operating speeds are increasing at such a fast rate that most products will soon exceed the digital/analog threshold. Digital signals traveling at high-speeds act like radio signals and passive circuit components, such as traces on circuit boards, become miniature "transmission lines". A large number of circuit components occupying very small areas act like transmitting and receiving antennas and create distorted signals that interfere with the operation of the digital circuit. There are thousands of digital signals that can be corrupted causing the electronic circuit to stop working permanently or intermittently. The only technique that avoids this increasingly serious problem is to consider impedance effects in the design of the PWB and to test ALL PWB's to verify Controlled Impedance design parameters.

Today, controlled impedance testing can not be done on 100% of PWB's because of cost and testing time. So PWB's are tested on a sample basis or by testing "coupons". Statistical sample testing is only practical if electronic manufacturers are willing to tolerate a specific failure rate. Test coupons are attached to the PWB and contain test point locations and "typical" trace lengths designed to accommodate today's manual probing methodology. Often the traces on these test coupons do NOT reflect the characteristics of traces on the actual PWB due to variations within the PWB manufacturing equipment. Also, these coupons add material and processing costs and reduce throughput capacity. Manual controlled impedance testing may induce inaccuracies and errors in the measurement process. Faulty PWBs may pass initial inspection, but cause unnecessary costs later in the manufacturing process.

The Controlled Impedance design requirements for PWBs are becoming increasingly stringent and are forcing PWB manufacturers to change their manufacturing processes and to increase the amount of Controlled Impedance testing. In the case of RAMBUS and other high-speed bus technologies , Dell and Compaq require 100% controlled impedance testing of all PWBs manufactured to ensure that the impedance of the board traces are within tolerance.

In summary, PWB manufacturers and their customers are faced with the following problems:

	Today's controlled impedance testing is done manually and is very slow and expensive.
	Testing requirements are increasing faster than can be accommodated by manual test techniques.
	Test accuracy and reliability requirements exceed the capabilities of manual testing.
	Manual testing often leads to work related injuries, because of repetitive motion operations.
	Test Coupons lead to reduced yields and often produce misleading results.

The Introbotics Solution

The Introbotics’ CI1000
Automated Controlled Impedance Tester

The Introbotics’ CI1000 Automated Controlled Impedance Tester solves the Controlled Impedance measurement problems by:

	Reduces testing time by a factor of nine, compared to manual testing methods.
	Increases accuracy of test results by a factor of ten, compared to manual testing methods.
	Increases throughput capability of testing by a factor of ten, compared to manual testing (less than 3 seconds per test, compared to 30 seconds per manual test).
	Increases the speed of setup by a factor of ten, compared to manual testing (test setup is 90 seconds or less, compared to about 15 minutes for manual testing methods).
	Reduces occurrences of health related problems such as repetitive motion injuries
	Faster, better process quality control information delivered by a flexible report writer over the customer's Intranet.
	Satisfies customer's engineering requirements

Payback

Any one of these factors alone can provide sufficient justification for a company's purchase of the product. A typical payback period on the purchase and operation of a CI1000 Tester is 6-9 months compared to manual controlled impedance measurement methods.

Testing with the CI1000 provides significant advantages over manual testing because robotic probe measurements eliminate errors that often occur with manual probing technique. The accuracy of robot positioning allows controlled impedance test probes to contact smaller pads on the actual boards. No longer will special test points or test coupons be required for board testing. Also, since the CI1000 can measure small trace lengths on the actual board, test results more accurately indicate board reliability.

INTROBOTICS CORPORATION
4208 Balloon Park Road NE Albuquerque, NM 87109
Tel: (505) 345-7785 Fax: (505) 345-7790 Email: info@introbotics.com