Test of HV Prototype Boards for LHCb Outer Tracker

NIKHEF, AmsterdamThe Netherlands

2003-10-16

HV Boards

Johanson Capacitors PCB Embedded

Working HV = 1,600V

Mass Production: 1,950

Test items:

Leakage Current

Capacitance

Micro-cracks inside Caps

x 32

Experimental Setup

HV to gnd net on HV boards may contributes to the measured leakage currents!

Experimental Setup (cont.)

HV = 2kV, Thermal Cycling = 20oC ~73oC,

Time = 24days, 15 boards are tested

Temperature Cycling • Temperature Cycle: 20oC 45 min.

20oC 73oC 15 min.

73oC 45 min.

73oC 20oC 15 min.

• Relative Humidity, not controlled, but kept low when temperature goes down

Due to unknown error of the temperature control system

Leakage Currents

Leakage currents of 15 boards are logged,

as well as the temperature and relative humidity

One Thermal Cycle

Left: with gnd net on HV board connected

Right: only 32 output pins of capacitors connected

Contribution from HV to gnd net on HV board:

~1nA@T=20oC and ~10nA@T=73oC

Correlation with Temperature and RH

Spread at T=73oC (T=20oC) is caused by time needed to warm up (cool down) the capacitors inside PCB

Not sensitive to RH anymore

Spikes

It is highly suspected that:

T goes down to <0oC due to unknown error;

ice formed on the board surface;

T goes up to 0oC, ice turns to be water to make board surface conductive

current spike occurs

Leakage current at T=20oC

Ileak of each board ↓

< 2nA, including the component from HV to gnd net on HV boards

Capacitance Measurement

• 480 Capacitors 479: ~30pF less than before

1: 187pF, 2/3 of other capacitors

• A crack found under microscope

Summary

Ileak of each board < 2nA after 24-day HV-on1 of 480 channels of capacitors has merely been b

roken by 24-day thermal cycling.Micro-cracks could be detected by thermal cyclin

g, although cycling conditions should be optimized by further study.