TEST COST REDUCTION CASE STUDY

REDUCING TEST EQUIPMENT INVENTORY BY USING A GENERIC AUTOMATION SOFTWARE / HARDWARE FRAME WORK

DOCUMENT NO 18/12/08 1/14

Originators

TEST COST REDUCTION IN RF BENCH : CASE STUDY PROPOSAL STAGE TO IMPLEMENTATION

System :

Sub-system :

Document Category

:

ABSTRACT

Approvals

Name of the Approver

HISTORY

Ed. 01 Proposal 01 18/12/08 <Initial Release>

TY JOSE

+91-484-2731265/2732924

+91-9952967626/9496276116

[email protected]/[email protected]



TABLE OF CONTENTS

TABLE OF CONTENTS.................................................................................................................................. 2

1 SCOPE ......................................................................................................................................................... 3

2 INTRODUCTION ...................................................................................................................................... 4 2.1 Purpose ................................................................................................................................................. 4 2.2 References ............................................................................................................................................ 4 2.3 Definitions, Acronyms and Abbreviations......................................................................................... 5

3 COST OF TESTING .................................................................................................................................. 6 3.1 Fixed Costs ........................................................................................................................................... 6 3.2 Variable cost ......................................................................................................................................... 6 3.3 Past Development ................................................................................................................................ 6 3.4 Cost reduction in Test Equipment Inventory (Specific to mobile hand set testing in Final

bench). ....................................................................................................................................................... 6

4 TEST ARCHITECTURES .............................................................................................................................. 7 4.1 SIMPLE TEST SET UP ......................................................................................................................... 7 4.2 EXTENDED SET UP MULTIPLE DUT SINGLE SET OF EQUIPMENTS ............................................ 8

5 SCOPE OF DEVELOPMENT ........................................................................................................................ 9 5.1 ADDITIONAL HARDWARE: .................................................................................................................. 9 5.2 SOFTWARE: ......................................................................................................................................... 9

6 IMPLEMENTATION OF THE STRATEGY IN LAST STAGE TESTING OF MOBILE HAND SET. ......... 10 6.1 HAND SET TEST FLOW ..................................................................................................................... 10 6.2 Test cases for mobile hand set in final bench ................................................................................ 10 6.3 Test instruments used for testing mobile in final bench ............................................................... 10 6.4 Mechanical design ............................................................................................................................. 10 6.5 Modifications done for equipment cost reduction. ........................................................................ 11 6.6 Test plan and equipments after sharing test equipments. ............................................................ 11

6.6.1 Keyboard tests ........................................................................................................................... 11 6.6.2 Audio testing .............................................................................................................................. 12 6.6.3 RF testing .................................................................................................................................. 12 6.6.4 Vision testing ............................................................................................................................. 12

7 CHALLENGES DURING DEVELOPMENT AND IMPLEMENTATION ...................................................... 13 7.1 RF Interference ................................................................................................................................... 13 7.2 Mechanical break down .................................................................................................................... 13 7.3 RF Relay failures ................................................................................................................................ 13

8 CONCLUSION............................................................................................................................................. 14



1 SCOPE

This document describes the objectives, technical, cost considerations and implementation for reducing the test cost of RF modules and RF ICs to aim drastic reduction of test cost and relative ease of implementation of test solution.

Details included for the implementation of the proposal in mobile receiver final stage testing and successfully achieved cost reduction.



2 INTRODUCTION

The commercial wireless/RF industry demands extremely low cost RF components and modules. The key contributor to the cost of RF ICs and Modules has been final test of device because of the need for complex single site testers and testing time. The main target for this study is achieving cost reduction in these stages.

2.1 Purpose

The cost of RF instrumentation is the major part of test cost. While using multiple instruments in test

bench, effective utilization of the free time of costly instruments will be a key cost saving factor. So sharing of instruments between multiple DUTs will be very effective. Planning for the low cost instruments for adaptable test cases will free up costly instruments and will save more test cost along with sharing of costly instruments between multiple DUTs.

2.2 References

S. No.

Document Version Date Author

1

2

3

4



2.3 Definitions, Acronyms and Abbreviations

UUT Unit Under Test (used interchangeably with term DUT or EUT)

EUT Equipment Under Test (used interchangeably with term UUT or EUT)

DUT Device Under Test (used interchangeably with term UUT or EUT)

SW Software

HW Hardware

LAN Local Area Network



3 COST OF TESTING

Test cost is driven by two main factors:

The fixed cost of test equipment and implementation based on test system capital, handler capital

and test hardware and software engineering development The variable cost per part based on test time, tester capacity, handler capacity, labor and operations

3.1 Fixed Costs

1. A handler /fixture cost of $300K, depreciated over 5 years. 2. An RF test set up costs between of $2M to $100K, depreciated over 5 years which includes costly

test equipments. 3. A cost of $50/Hr to run the manufacturing floor and maintain and operate the testers. 4. A cost of $150K for hardware development of a unique RF test solution spread over a 2 year product

life.

3.2 Variable cost

Test time and labor contributes to variable cost.

3.3 Past Development

Past lot of developments were taken place to cut down the testing time by re sequencing and simplifying test modules, re molding the test adapters. The test equipment inventory is an area needs improvement. Since most of the testers use multiple equipments and multiple routine, it’s possible to share the costly equipments between testers. The evolution of PXI and LXI platforms made this fast and simple for implementation.

3.4 Cost reduction in Test Equipment Inventory (Specific to mobile hand set

testing in Final bench).

1. By hooking up multiple test stations to single equipment : To utilize idle time of equipments

while test software is engaged on other routines and engaging the test equipment during handling time on test fixture

2. Engaging less costly equipments wherever possible. : Like using a USB Power Sensor ($2500 ) for radiated Tx Power measurements , sparing costly communication tester($80K) to other testers hooked up with the same system or reading SIM from phone memory instead of checking SIM through establishing a call situation which utilizing costly Communication Tester

3. Optimizing Test Plans, Eg: TX and Rx paths will be fully tested during previous test stage, PA and Rx calibration. Exploring possibility of minimizing repeated verification of Rx and Tx paths using communication tester.



4 TEST ARCHITECTURES

Below is a comparison on test architectures while simple testing and multiple DUTs Hooks to single RF test equipment.

4.1 SIMPLE TEST SET UP

In this set up single UUT is connected a set of RF equipments

PC - Initialize tester, Analyze data, Pass/fail, store data

RF MEASURING

INSTRUMENTS

DATA BASE

TEST FIXTURE WITH

HAND SET (DUT)

LA

N

GPIB RF

DATA



4.2 EXTENDED SET UP MULTIPLE DUT SINGLE SET OF EQUIPMENTS

In this set up the RF equipments are shared between Multiple DUTs.

PC - Initialize tester, Analyze data, Pass/fail, store data

RF MEASURING

INSTRUMENTS

DATA BASE

TEST

FIXTURE

WITH HAND

SET (DUT)

1

LA

N

GPIB

RF

DATA

TEST

FIXTURE

WITH HAND

SET (DUT)

N

RF /DATA

MUX

DATA

RF

DATA

RF



5 SCOPE OF DEVELOPMENT

5.1 ADDITIONAL HARDWARE:

1. RF MUX - Agilent relay (can work up to 27 GHz) with TTL to serial/USB/LAN/GPIB interface. 2. Analog MUX from NI

5.2 SOFTWARE:

The existing test software needs to be re organized for effective sharing of the test equipment. Supervisory application should be configured using Test stand with multiple executions.


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6 IMPLEMENTATION OF THE STRATEGY IN LAST STAGE TESTING OF MOBILE

HAND SET.

The test strategy is implemented in mobile hand set testing in final bench. The units coming to this stage will be completed board level testing and alignement. Tested boards are assembling in handset covers including LCD and key pad.

6.1 HAND SET TEST FLOW

FLASHING

TEST

APPLICATION

TX, RX &

ANALOG

CALIBRATION

AND TESTING

ASSEMBLY FINAL TETSINGLABELING AND

APPS LOADING

6.2 Test cases for mobile hand set in final bench

Key pad verification

LCD display and LED verification.

Audio testing including mic and speaker

RF verification after enclosure. Call generation / and radiated power measurement.

Power supply

6.3 Test instruments used for testing mobile in final bench

Mechanical arrangement for key pad simulation – low cost

CCD cameras with Vision software

Audio generator

Bench power supply

Communication tester CMU200/8960- very high cost

6.4 Mechanical design

The set up is designed to operate four to eight test stations by a single operator to cut down operating cost.


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6.5 Modifications done for equipment cost reduction.

It has been observed that the cost of testing in bench is mainly contributed from communication tester CMU 200/8960.This equipment is in use only 25% of the total test time. Apart from call simulation test the radiated power can be measured using low cost USB power sensors.

Integrating four test stations to a single bench having single computer with software for multiple executions.

Audio testing equipments are replaced NI PCI card and an audio switch to cut down cost for four stations- multiplexing a single card for four stations.

Standard bench power supply is replaced by a tailer made low cost synthesised power supply.

The communication to handset is remains unchanged with serial, providing additional PCI serial cards for each bench.

Introduced 4 ports two ways RF switch. Sharing USB power sensor and communication tester for four test stations.

Test bench is enclosed with RF shield box to achieve RF isolation between benches.

6.6 Test plan and equipments after sharing test equipments.

6.6.1 Keyboard tests

The functionality of the keyboard is tested to ensure that the DUT’s buttons are working properly. This is done by pressing the buttons with small pneumatic cylinders. The results are


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buffered in the phone and then sent as a string to the IPC measurement card. The keyboard lighting is also tested with a LDR, with the test result depending on the voltage level.

6.6.2 Audio testing

For the use of audio testing, the test mechanics contain a microphone and loud speaker installed.

Microphone testing is carried out as follows. An audio signal (e.g. 1 kHz) is generated by the NI PCI DAQ board 6502 routed with the audio switch box and is then connected to the loudspeaker. The DUT microphone is used to collect the audio signal and it is then read back using the x-ear connection on the lower adapter. The signal is further routed to measurement card via audio switch box to be analyzed.

To test the DUT speaker, the signal is generated in the IPC measurement card and fed to the DUT by x-mic connection (lower adapter). It is then outputted from the DUT speaker and collected with the microphone located in the upper adapter. The signal is then linked by the audio switch box to the NI 6502 measurement card.

6.6.3 RF testing

The RF characteristics of the DUT are tested with cellular tester and power sensor.

6.6.4 Vision testing Purpose of the vision testing is to identify possible defects in the DUT display. The display is tested using a camera and machine vision software

With the display back light powered, the tests are run in states when all the pixels are turned on, and when they are all switched off. If pixel rows are active when they should be inactive and vice versa, the test will result to fail.

Keyboard back light is tested by LDR located between pneumatic fingers in upper adapter.


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7 CHALLENGES DURING DEVELOPMENT AND IMPLEMENTATION

During the trial implementation major challenges faced are RF interference between the DUTs and

Mechanical breakdown of moving parts within the test box.

7.1 RF Interference

Four DUTs are running in parallel in a staggered manner of test cases for utilizing the instruments very effectively. During radiated power measurement the handset will transmit 20 dbm power approximately. Rx sensitivity measurement is happening at -90 dbm. During initial trial testing of the system Rx PER measurement errors are observed randomly. On detailed analysis it’s found that TX radiation from adjacent DUT is causing the failure.

The measurement of shielding effect of test boxes were done, it was from 40- 45 db. Improvement is done on the shield box with the following.

Changing RF gasket at the openings with high quality gasket material.

RF and Data connectivity to the test box changed with wave guide interface.

These modifications resulted in 5 - 10 db improvement in attenuation in shielding and the random failure issue resolved.

7.2 Mechanical break down

Since shield box opening and closing were automatic, magnetic proximity sensors were provided to protect the chance of injury for operator hands.

During initial trials it’s noticed that the sensors are getting damaged with contact with mechanical parts. This is resolved by repositioning sensors. Found its meeting the requirement.

7.3 RF Relay failures

Initial build solid state RF relay with LAN interface is used for multiplexing RF signals different DUTs. During trial run it’s noticed LAN interface board is getting corrupted causing mal functioning of the relays. Also failure of the relay drivers noticed.

To overcome the situation we have replaced the relays the conventional RF relays from Agilent with GPIB drivers. Resulting in stable operation of the test system.


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8 CONCLUSION

This test strategy has been found acceptable for mass production and very effective in with respect to cost reduction. The test system is designed for single operator will handle multiple test DUTs adding overall cost reduction.

END OF DOCUMENT

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