Rapid data acquisition for the analysis of small gas volumes

International Journal of Mass Spectrometry and Ion Processes, 60 (1984) 251--264

251

Elsevier Science Publishers B.V., A m s t e r d a m -- Printed in The Netherlands

RAPID DATAACQUISITIONFOR THE ANALYSIS OF SMALL GAS VOLUMES

L.J. RIGBY, Standard Telecommunication Laboratories Limited, London Road, Harlow, Essex. ABSTRACT Failure of encapsulated transistors can often be attributed to a high water content, and gases such as hydrogen, carbon monoxide oxygen and halocarbons can influence device characteristics. Mass spectrometry provides the only d e f i n i t i v e , albeit destructive test, of these and similar components. By subjecting the device to a high pressure of a suitable tracer gas before analysis, package hermeticity can be tested to below lO- l l atm.ml/s. Quantitative transfer of the sample gas to the detector requires a carefully designed analytical procedure. The equipment which has been developed to meet this requirement uses a microprocessor to control gas transfer to a quadrupole mass spectrometer and to r e p e t i t i v e l y acquire and process mass spectra.

I NTRODUCTI 0N Electronic packages are hermetically sealed in inert gas atmospheres in order to prevent degradation of sensitive electrical elements by active gaseous species.

Packages which are not hermetic or inadvertently contain

additives such as cleaning solvents, poorly cured resins, residual moisture etc. are potential causes of device malfunction.

Excessive water vapour

provides surface layers in which spurious electrical conductivity and ion migration may eventually lead to corrosion and f a i l u r e .

Corrosion may be

enhanced by ionic or potentially ionic species such as carbon dioxide, hydrogen chloride or organic halides.

Active surface layers may be influenced

by atmospheres which are predominantly oxidising or reducing and low concentrations of a seemingly innocuous gas can result in eventual f a i l u r e . good example of the l a t t e r is the transport of nickel by carbon monoxide as nickel carbonyl from the l i d of a package to the surface of an active device. A complete analysis of a package atmosphere should therefore be an essential part of quality control in high r e l i a b i l i t y devices and should be the f i r s t part of a device f a i l u r e examination.

A well designed mass

spectrometer system is the only method available for a complete gas analysis of small gas volumes,l

High analytical r e l i a b i l i t y may be achieved with

good quality instrumentation backed by a precise and rapid data acquisition system and a consistent calibration procedure. 2

0168-1176/84/$03.00

© 1984 Elsevier SciencePublishers B.V.

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252

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Fig. 1 Schematicdiagram of sample chamber (SC) and Baratron gauge (B) with gas supply from a 3 volume calibration valve (3VCV). The quadrupole mass spectrometer (MS) and the sample chamber are maintained at lO0OC and are pumped by two turbomolecular pumps (TP) monitored by ion gauges (IG) and backed by a commonrotary pump (R2). Rotary pump Rl is used to i n i t i a l l y pump SC via V3. D is a direct reading mirror hygrometer. APPARATUS The hardware was designed and b u i l t by the Pernicka Corporation. Figure 1 is a schematic drawing of the essentials.

Computercontrolled valves VI-V3

allow the sample chamber to be evacuated to a base pressure of 2 x lO-8 torr then sample gas to be introduced into the sample chamber and quantitatively transferred through a Nupro SS-4BG controlled leak (V2) to the ion source of a Balzers Q311 quadrupole mass spectrometer. Calibration gas volumes of O.Ol, 0.1 and 0.75 ml from the 3 volume calibration valve may be admitted through V4.

The stainless steel walls of

the total gas analysis system are maintained at a constant IO0°C to minimise the effects of reversible water adsorption.

Small packages of less than l ml

internal volume are loaded in batches of 12 on a carousel which can be rotated under a suitable puncture head. Larger metal packages can be mounted externally by clamping over a small Viton 0 ring so that the puncture needle can penetrate the metal wall without disturbing the O-ring seal.

253

GAS TRANSFER The controlled leak V2 is preset to maximise gas transmission through the mass spectrometer.

A high transmission allows most of the gas sample to

traverse the mass spectro~ter ion source and provide acceptable transfer curves for condensible species such as water.

The l i m i t on V2 is the maximum

allowable pressure of about 2 x lO-5 torr in the mass spectrometer as nonlinear ion currents result from higher pressures. Table l shows the V2 settings for gas volumes up to 30 atm.ml for a sample chamber volume of 184 ml. is independent of quantity.

The conductance of V2 controls gas consumption and The effusion rate (S) can be calculated from the

time taken to reduce the pressure p by one h a l f the original value (Po) as the decay in pressure is given by: In p/Po = - St/V where V is the sample chamber volume, so that S = V In 2 / t l / 2 When the largest conductance is used for gas samples of less than 0.2 atm.ml, over 99% of the gas effuses through V2 in less than 2.4 minutes and rapid measurements with minimum signal averaging are required to obtain all the available data.

Analysis times are extended for larger gas samples, and for

gas contents above 2 atm.ml sample consumption f a l l s to less than 80%. These times could be extended further but times in excess of 20 minutes become uneconomic and package contents of greater than 2 atm.ml are rarely encountered.

Pressure measurements show that transport is by molecular flow

for samples of l atm.ml or less, but for quantities in excess of 5 atm.ml the flow is predominantly viscous.

Flow considerations are unimportant provided

TABLE l GASEOUSTRANSFERPARAMETERSFOR QUANTITIESUP TO 30 ATM.ML. Maximum I n i t i a l Vernier I n i t i a l quantity chamber setting quadrupole in ai~.ml pressure of V2 pressure in in torr torr x lO-5 0.2 0.5 1.0 2.0 8.0 30

0.84 2. l 4.2 8.4 34 130

160 lO0 50 25 lO 0

l .5 1.8 1.6 1.6 1.5 1.7

Time to Effusion Analysis % consumed consume rate in time in in the 50% of gas ml.s m i n u t e s allotted sample in time seconds 17 22 88 185 482 2390

1.53 0.84 0.30 O. 14 0.05 O.Oll

3.1 3.6 6.2 9.0 9.0 16.4

lO0 99.8 99.3 82 52 21

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TABLE 2 The following l i s t relates the 32 ions routinely monitored to the possible sources of each ion: 2or3 4 7 12 15 16 or 8

+

÷

H2 or HD from hydrogen He+ from helium N++ ion from nitrogen C+ from carbon monoxide and carbon dioxide 15N+ (nitrogen), NH+ (amlnes), " + (hydrocarbons) CHR 0+ or 0++ (oxygen), 0+ (water), NH -+2 (amines), CH4 methane 17 OH+ (water), NH3 (ammonia) 18 H2O+ (water) HOD+ (water), F+ (fluorocarbons and HF) 19 Ne+ (neon), Ar++ (argon), HF+ (hydrogen fluoride) 2O Ne+ (neon), C02+ (carbon dioxide) 22 ÷ 26 C2H~ (hydrocarbons) C2H~ (hydrocarbons), 14Nl5N+ (nitrogen) 29 C2H6 (ethane), 15NISN+ (nitrogen), CH3NH (amines) 30 + (alcohols), CF+ (fluoro compounds) 31 CH~O 32 or 34 02 (oxygen), S (sulphur compounds) ÷ C1 (ch]orlne compounds) 35 36Ar (argon), HCI+ (hydrogen chloride) 36 37 Cl + (chlorine compounds) + (Unsaturated hydrocarbons) 38 HCI+ (hydrogen chloride), C3H2 39 C3H3 (aromatics and unsaturated aliphatics) ÷ 40 Ar (argon) ÷ ÷ . . 41 C3H5 (hydrocarbons), CH3CN (nltrldes) ÷ 42 CHpCO (lactones, furans, ketones, aldehydes) -÷ + 43 C~H7 (hydrocarbons), CHACO (ketones) -+. . ÷ . 44 CO2 (carbon dloxlde), C2H4NH2 (amlnes) 45 C2H50+ (alcohols, diols, ethers) ÷ . . . . NOp (nltrogen dloxide, organlc nltrates) 46 -÷ ÷ ÷ 47 CCI (chloro compounds), COF , C2H4F (fluoro compounds) 48 SO+ (sulphur compounds) 49 CC1+ (chloro compounds) 50 CF~ (f]uoro compounds), C4H2 (aromatics)

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that total gas transport is achieved by uniform pumping of the mass spectrometer ion source so that integration of a l l the ion current/time curves may be l i n e a r l y related to the quantities of each species consumed. Partial consumption may be tolerated i f the pressure decay curves of sample and standard are similar.

Indeed the r e l a t i v e s e n s i t i v i t y of the mass spectro-

meter to a l l permanent gases is not affected by changes in transportation rate or percent consumption. More care is required with condensablespecies such as water, and analysis times have to be extended so that the curve of the mass 18 ion current shows a reasonable decay characteristic.

This is of particular

importance when slow evolution of water occurs from packages containing porous and/or hygroscopic surfaces.

In these cases, an inspection of the

transportation curves can yield additional information regarding the nature of the package.

DATA ACQUISITIONAND PROCESSING Analogue signals from the mass spectrometer electron multiplier and the pressure gauges are multiplexed to a dedicated Midas IV microprocessor capable of d i g i t a l l y reading O-lO V signals with a resolution of l mV at intervals of I ms.

Overall control of data transfer resides with a Hewlett-Packard 9825

computer which instructs Midas to open or shut valves and obtain all the necessary data. Admission of a gas sample to the sample volume triggers a sequence in which V2 is opened and cyclic readings of gas pressure in the sample volume and each of 32 selected ion currents (as listed in Table 2) are read.

A minimum of 5

readings is taken at each point in the cycle and averaged. Normallyafter the second cycle, a sensitive mass scan is madebetween masses 51 and 97 to cover the whole of the available mass range. The analysis is complete in 20 cycles in a time which may be extended from 3 to over 16 minutes depending on the quantity of the gas sample. Digital clock readings are also stored during the analysis sequence so that area measurementof each ion current/time curve is a quantitative estimate of the sample transfer process which can be d i r e c t l y related to similar data obtained with suitable gas standards.

INITIAL PROCEDURE: TEST FOR HERMETICITY An essential part of the analysis is a test of hermeticity.

Conventional

leak detectors measure the rate of helium effusion from a package which has been pre-immersed in a helium bomb. This test is non-destructive and is

256

amenable to batch processing but the l i m i t of detection is only l x lO-8 atm.ml/s and corresponds to a 50% exchangeof gas ambient in a package volume of O.l ml in a period of only 6 weeks. Leaks greater than lO4 atm.ml/s require alternative methods and may not always be detected.

Mass

spectrometric analysis of the tracer gas which has diffused into the package is able to detect leaks of at least l x lO-lO atm.ml/s.

A simplified

measure of the leak rate can be obtained by assuming a unidirectional linear flow of helium through the leak into the package. Then the leak rate in atm.ml/s is given by: L = Barometric pressure x % of Helium found x Total gas (atm.ml) Helium soak pressure

IO0

Soak time (s)

and the detection of lO ppm of helium in a gas volume of l atm.ml after a 16 hour soak time in 2 atmospheres of helium results in a leak rate of 8.7 x lO- l l atm.mls.- l

A package having this leak rate could experience a I0%

gas interchange in a period exceeding 4.4 years.

Immersion and subsequent

detection of other gases, e.g. krypton, becomes more appropriate when glass envelopes (which diffuse helium) are under investigation.

In addition, the

presence of a high water content and oxygen in packages known to have been encapsulated in a dry oxygen-free environment are good indicators of non-hermetic i t y . The whole of the upward range is simultaneously catered for by a measurement of helium content and total gas content.

Leaks greater than

lO-2 atm.ml/s would be identified in small packages as an absence of sample gas which would be lost during the i n i t i a l pump down procedure. Larger packages which are externally mounted may not release any helium which had time to effuse from the package before analysis, but would release moist air and would subsequently respond to an external probe of helium gas.

A

temperature ramp to 200°C is normally included in the bombing period to show fine leaks which may be sealed at ambient temperature by constriction or blockage.

SAMPLE LOADINGAND ANALYSIS The test apparatus is evacuated at temperature for a minimum of 16 hours so that the pressure in the mass spectrometer is below l x lO-9 torr before analysis and the sample chamber pressure is in the region of l x lO-8 t o r r . After sample loading and setting the transfer conductance of V2 according to Table l , accurate reproducibility is achieved for all samples and standards by a cyclic process which is under the direct control of the main computer.

257

Surface conditioning of the walls of the sampling system is an essential part of reproducible and quantitative water analysis.

For this reason and to

optimise mass spectrometer s e n s i t i v i t y , an i n i t i a l short run is carried out before the analysis of each sample, with a volume of room air which is similar to the expected sample volume and is introduced when the background pressure in the sample chamber has fallen to 4 x lO-8 torr.

After this i n i t i a l

conditioning, the quadrupole electron multiplier voltage can be adjusted i f necessary to set the measurementrange of the instrument for maximum s e n s i t i v i t y without saturation.

When the repumped sample chamber pressure

reaches 3 x lO-8 t o r r , the i n i t i a l run is repeated so that residual ion currents can be monitored.

Unusual increases in, for example, the mass 32

(oxygen) and mass 4 (helium) ion currents at this stage can provide an early indication of a non-hermetic package or an external air leak and the appropriate remedy can be applied as necessary. ~en, on repumping, the sample chamber pressure f a l l s to 3 x lO-8 torr, the operator is prompted to release the appropriate gas sample. A quick i n i t i a l scan indicates what the major components are and therefore which isotopic masses are to be measured. Normally, packages are nitrogen f i l l e d and so the 14N 15N ion current at mass 29 is suitable.

Similarly

concentrations of argon, oxygen and water above a few percent are overrange at the major molecular isotope and force measurement at masses 36(36Ar),34(160180) and 19 (HDO) respectively.

Overrangemay also occur

at the minor isotopes but these are usually small and estimates of actual values can be made by back extrapolating the decay curve from the l a t e r , on-scale values. Cyclic readings and a high mass scan are then obtained as outlined in Section 4.

Whenthe data have been stored the sequence may be repeated for

the remaining samples.

STANDARDISATION Standard gas mixtures are required for calibration of the mass scale and determination of ion current sensitivity. Eight ion currents are used to determine the mass scale.

A suitable

mixture of hydrogen, helium, carbon dioxide and trichloroethylene in air is used for calibration points at masses 2, 4, 12, 22, 34, 47, 61 and 97.

The

quadrupole is tuned for minimum, but adequate, resolution to achieve high s e n s i t i v i t y and high s t a b i l i t y .

Under these conditions the mass scale is

stable to within ~ 0.2 mass units over periods of several weeks.

258

Known concentrations of hydrogen, helium, oxygen, argon and carbon dioxide in nitrogen provide a suitable quantitative standard for the major gases. Instrument s t a b i l i t y is such that weekly measurements show s e n s i t i v i t y changes of less than 5% for all of these gases and most of the variation can be attributed to measurement error rather than true deviations in s e n s i t i v i t y .

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Fig. 2 Water calibration for gas volumes of O.l and O.Ol atm.ml and needle valve settings of 50,I00 and 160.

259

Calibration for water vapour is made on a same day basis because s e n s i t i v i t y to water is a function of transfer rate and the amount of variable surface area in the sample chamber.3 Rapid extraction of a known volume from a flowing gas stream is required and can be readily obtained with the 3 volume calibration valve. 4

Good correlation has been obtained with gas

streams from either a general purpose humidifier* or mixtures of laboratory air and nitrogen.

Wet and dry bulb measurements were used for estimations Of

the water content in the laboratory air samples used to provide the data for Figure 2 which show that good l i n e a r i t y can be obtained above 0.1% (I000 ppm).

An i n l i n e mirror dew point hygrometer is currently in use to determine

the water content in standard samples.

INTERFERENCES AND DETECTION LIMITS Adsorption and replacement at metal surfaces and reaction at hot fi]aments can cause significant deviations to low concentrations of several components. These effects are minimised by running a coated iridium mass spectrometer ionisation filament at a low emission current of 0.2 mA and surface pretreatment with room a i r .

Oxygen is the most reactive gas usually

encountered and i t was found that 0.75 ml of the pure gas released 0.19% water, 0.044% carbon dioxide and 0.004% carbon monoxide. Fortunately, for 20% oxygen in nitrogen, these values are reduced to 0.02, O.Ol and 0.004% respectively.

No other chemical effects were observed but electron impact

fragmentation of molecules and subsequent ion-molecule reactions inevitably produces lower molecular weight ions which have to be accounted for. For + example, nearly 4% of ionised water is analysed as H2 and 30% results in OH+ having the same mass as NH;. Table 3 ] i s t s the major gases for r e l a t i v e s e n s i t i v i t y and detectability.

The quoted detection limits assume

absence of interferences in the gas mixture and optimum s e n s i t i v i t y . Reference to Table l w i l l indicate that s e n s i t i v i t y should f a l l when the maximum quantity of available gas drops s i g n i f i c a n t l y below 0.2 ai~.ml.

As

the conductance cannot be increased further, s e n s i t i v i t y declines in proportion to f a l l i n g ion currents and electron multiplier noise.

In

practice, the smallest quantities yet analysed were 0.002 atm.ml and yielded detection limits which were about I0 times greater than those shown in Table 3. * In a general purpose humidifier, water vapour saturates a carrier gas at high pressure. The carrier gas pressure is then reduced to atmospheric pressure and as the water content remains the same, accurate low levels of water partial pressure can be obtained.

260

TABLE 3 TYPICAL SENSITIVITY FACTORSAND DETECTION LIMITS IN A O.l ATM.ML GAS SAMPLE Gas

Hydrogen Helium Carbon monoxide Methane Ammoni a Water Nitrogen " Oxygen Argon Carbon Dioxide

Mass

Relati ve sensitivity

2 4 12 16 17 18 28 29 32 40 44

45 19 15 95 40 58 lO0 0.74 87 84 190

A B C D E F G H I

u~

-,-.

Detecti on l i m i t in ppm

Inter fer ence

lO lO 50 5 200 500 5

Water None CO2 02, N2 Water 02 CO,CO2, Organics Organics None None 02

5 5 5

Typicat nitrogen decay (m a ss 29) 2 . 0 % w a t e r (mass 18) 0.95 % 0.83% 0.52% 0.30% 0.09"•, O. 01% O. 00%

3

o

:>

D D

o

2

H-...~ 20

4(3

60

80 Time

100

120

140

160

(sec o n d s)

Fig. 3 Water Transmission from TO5 packages with V2 setting=lO0

261

TABLE 4 TABULATEDDATA FOR 0.2 ML PACKAGE MS File No. 12 Component

Total Gas Content = 0.23 atm.ml Needlevalve set to lO0 % Composition

Water Hydr ogen Hel i um Nitrogen Oxygen Argon Methane Carbon Monoxide Carbon Dioxide

0. 149 0.062 <0.0040 99 0.0012 0.0008 <0.0008 <0.0060 0.0197

Other Masses 30 19 26 31 42 43

% Rel. Comp. < 0.0034 <0.003 l 0.0017 O.OOll O.OOll 0.0014

NOTES Helium content is equivalent to a leak rate of l . I E - l l atm.ml/sec. MS File No. 13 Component

Total Gas Content = 0.23 atm.ml Needlevalve set to lO0 % Composition

Water Hydrogen Helium Nitrogen Oxygen Argon Methane Carbon Monoxide Carbon Dioxide

l . 16 0.040 0.68 96 0.98 0.061 0.0032 <0.0040 0.070

Other Masses 22 30 19 20 26 31 35 39 41

% Rel. Comp. <0.0019 <0.0046 <0.035 <0.0115 0.0018 <0.0095 0. O01l 0.0015 0.0009

NOTES Helium content is equivalent to a leak rate of 6.6E-09 atm.ml/sec.

EXAMPLES Figure 3 shows typical water transmission characteristics at lO0°C. The packages were size TO5 containing a silicon transistor. content was from 0.230 to 0.235 ai~.ml.

The measured gas

The decay curves uniformly approach

curve I which was obtained with an equivalent volume of dry nitrogen.

This

curve has a small positive slope which results from the slow release of water molecules pre-adsorbed on the surfaces of the sample chamber during the i n i t i a l preconditioning by air exposure. Water levels are calculated by subtracting the area under this curve from the area obtained for each sample, and the l i m i t of detection for water is reached when this background becomes significant.

All the water decay curves are not surprisingly less steep than

the corresponding curve for nitrogen.

Area measurements for all curves are

terminated at the last measured point in an admittedly arbitrary fashion. However the alternative is to extrapolate to a suitably chosen baseline and

262

TABLE 5 TABULATEDDATA FOR 0.2 ML PACKAGE MS File No. 21

Total Gas Content = 0.0019 ai~B.ml Needlevalve set to lO0

Component

% Composition

Water Hydrogen Hel i um Nitrogen Oxygen Argon Methane Carbon Monoxide Carbon Dioxide

Other Masses

l . 82 1.67 0.0300 96 0.03 l 0.0060 0.0050 0.0300 0.58

19 26 39 43 50 51

% Rel. Comp. < 0. 024 0.023 0.0172 0.0160 O.022 0.037

NOTES Helium content is equivalent to a leak rate of 6.3E-I0 atm.ml/sec. MS File No. 22 Component Water Hydrogen Helium Nitrogen Oxygen Argon Methane Carbon Monoxide Carbon Dioxide

Total Gas Content = 0.0013 atm.ml Needlevalve set to lO0 % Composition 9.0 I. 35 O. 35 83 4.6 0.47 0.0030 0.0200 1.31

Other Masses

_

22 19 20 26 39 43 45 50 78

% Rel. Comp. <0.0099 <0.030 <0.058 0.02 l O.037 O.032 0.0170 0.026 0.071

NOTES Helium content is equivalent to a leak rate of 1.8E-08 atm.ml/sec.

may introduce errors, particularly when non-ideal curves are encountered. The present method does readily discriminate between different levels of moisture even though accuracy may become more d i f f i c u l t at concentrations below say 500 ppm. Examples of f i n a l reports, as printed out by the computer, are reproduced in Tables 4-6.

In these reports, the percent compositions of the usual

components are obtained from the selected ion currents and their r e l a t i v e sensitivity factors listed in Table 3 after taking into account possible interferences from other species as discussed above. A l i s t of detected other masses is produced by assuming unit s e n s i t i v i t y of all of these with respect

263

TABLE 6 TABULATEDDATAFOR 0.2 ML PACKAGE MS File No. 25 Component Ammonia Water Hydrogen Helium Nitrogen Oxygen Argon Methane Carbon Monoxide Carbon Dioxide

MS File No. 27 Component Ammonia Water Hydrogen Helium Nitrogen Oxygen Argon Methane Carbon Monoxide Carbon Dioxide

Total Gas Content = 1.72 atm.ml Needle valve set to 25 % Composition 0.0096 0.56 0.0007 0.0020 99 0.0023 0.0079 0.0070 0.0130 0.032

Other Masses 22 30 19 20 26 31 35 36 37 38 39 41 42 43 45 46 47 48 49 50 64 66

% Rel. Comp. 0.0057 0.0074 0.0051 0.0051 0.0179 0.0066 0.0015 0.0008 0.0013 0.0015 0.0041 0.0060 0.0050 O.Oll2 0.0022 0.0008 0.0017 O.OOll 0.0054 0.0013 0.0190 0.0059

Total Gas Content = 1.75 atm.ml Needle valve set to 25 % Composition 0.093 2.2 O.OOlO 0.0030 97 0.0024 0.0185 0.0200 0.043 0.28

Other Masses

% Rel. Comp.

22 30 19 20 26 31 37 38 39 41 42 43 45 46 49 50 55

0.0007 0.0044 0.0056 0.0018 0.0155 0.0183 0.0034 0.0053 0.0193 0.041 0.041 0.043 0.0128 0.0034 0.0009 0.0036 0.0123

264

to nitrogen.

Table 2 indicates that some of these could result from the

isotopes of major impurities (e.g. HDO+ at mass 19, N15 N15 at mass 30), s p i l l over of large peaks (e.g. an apparent mass 31 from a very large mass 32 ion current), or doubly charged ions (CO~+ at mass 22) and these effects are usually denoted by a < notation.

The remaining ions of significance

usually indicate the presence of other species which are normally organic in ori gin. Table 4 shows comparative results from two TO5 packages. The present U.S. 883B M i l i t a r y Specification for water in encapsulated devices is 5000 ppm. The top set of data in Table 4 show a comfortably lower water content of ll50 ppm, low oxygen and carbon dioxide.

The absence of helium indicates that

hermeticity is better than l . l x I0 - l l abn.m1.s- l .

A helium content of

0.68% in the lower data correspond to a fine leak of 6.6 x lO-9 abn.ml.s - I This is confirmed by higher levels of oxygen, water, argon and carbon dioxide which may a11 be attributed to air ingress. Table 5 shows similar sets of data from very small diodes of less than 0.002 abn.m1.

All detection limits are higher than those quoted in Table 4 but leak

rates down to 7 x lO-lO atm.ml .s - l are s t i l l measurable. These devices had been subjected to a damp heat test so i t is not surprising that 9% water had accumulated in a non-hermetic device. Table 6 shows data which were obtained for two larger packages containing epoxide adhesive.

Large quantities of water with detectable amounts of ammonia

and several organic species can be attributed to a poorly cured adhesive.

These

results i l l u s t r a t e the need for a careful choice of a high quality resin and prolonged post baking procedures to minimise a potential source of harmful vapours in hybrid packages.

ACKNOWLEDGEMENTS The author thanks STL Ltd for permission to publish this paper.

REFERENCES I . R.W. Thomas and D.E. Meyer, Solid State Technology,17 (1974) p56-58. 2. J.C. Pernicka and B.A. Raby in the Proceedings of the NBS/RADC Workshop, Nov. 1980; US National Bureau of Standards. Special Publication 400-72, p3. 3. R.L. Perkins, ibid pS. 4. B.A. Moore, ibid p39.