Research on Over-Temperature using of PEM Evaluation Method in

Military

Xuliang Wang

, Yuan Liang

2, a

93128 PLA TROOPS, 14#, Fuxing road, Haidian district, Beijing, China

Equipment Department, China Aero-Polytechnology Establishment, Jingmi Road 7#, Chaoyang district, Beijing, China

Keywords: PEM, over-temperature, reliability.

Abstract: In order to evaluate the reliability of over-temperature using of Plastic Encapsulated Microcircuit (PEM) in

military, this paper designs tests to simulate environmental suitability and lifetime by analyzing the failure

mode and mechanism of PEM (the plastic encapsulated microcircuit). Based on the analysis, the evaluating

tests are designed and conducted, and the result shows that HAST (High accelerated stress temperature),

temperature cycling, and Steady state life test under the operating condition but within the maximum

temperature limit, can be chosen to evaluate the reliability of the devices used over-temperature in sequence.

This provides a set of feasible evaluation methods for the over-temperature using of PEM, which can

effectively guarantee the quality and reliability of PEM, also provides theoretical basis for the subsequent

formation of effective evaluation methods and standards for the screening and detection of the over-

temperature using of PEM.

1 INTRODUCTION

Plastic package is the main form of electronic

components packaging, for its low cost, small size as

well as light weight, etc. It is a statistical fact that

92% of IC components and discrete devices use the

plastic package at present.

As the moisture absorption and the mismatch of

thermal expansion coefficient of epoxy resin, the

plastic encapsulated microcircuit (PEM) is generally

limited to apply in the field of aerospace, military

and high reliability industry. One of the most serious

problems is its narrower temperature range.

Comparing with the glass and ceramic,

encapsulation materials belong to low temperature,

and its vitrification transition temperature is between

130~160°C, it mainly satisfies the requirement of

the temperature range of the 3 followings: 0°C

~70°C (commercial), -40°C ~85°C (industrial) and -

40°C ~125°C (car), all the 3 temperature ranges are

narrower than military temperature range (-55°C

~125°C). Besides, there are many other application

environments that are even more extreme, such as

cold climate of avionics and spacecraft requires -

65°C or less, and the ignition control is up to 175°C,

even the aviation electronic distribution control

system reaches 225°C. If the PEM is directly used in

target temperature conditions without evaluation and

assessment, it usually causes problems such as high

failure efficiency and low reliability of electronic

products (LIANG Yuan, et.al, 2015). Therefore, it is

urgent to establish an evaluation method and

procedure for the over-temperature using of PEM to

ensure the quality and reliability, which can provide

theoretical basis for the subsequent formation of

effective evaluation methods and standards for the

screening and detection PEM in over-temperature

using.

2 FAILURE MODE AND

MECHANISM ANALYSIS OF

OVER-TEMPERATURE USING

OF PEM

Recently, the PEM reliability has greatly improved

along with the progress of the packaging materials

and coating process, while the reliability

requirement is much higher, but the main failure

mode for PEM is still delamination, especially

serious for the plastic power device with hermetic

408

Wang, X. and Liang, Y.

Research on Over-Temperature using of PEM Evaluation Method in Military.

DOI: 10.5220/0008868204080412

In Proceedings of 5th International Conference on Vehicle, Mechanical and Electrical Engineering (ICVMEE 2019), pages 408-412

ISBN: 978-989-758-412-1

problem in the condition of high temperature with

high voltage and large current. In the process of

reliability testing and servicing, it is common to find

delamination between epoxy molding compound

(EMC) and the lead frame, as well as the micro-chip

and substrate, which leads to a series of failure

modes, such as plastic strain crack, passivation layer

damaged, leakage current increased, PN junction

damaged, etc (AndrewA.O.Tay, 1996).

Normally, there is boundary layer (transition

layer) between the copper substrate and epoxy

molding compound (EMC) in PEM. The transition

layer, different with other part of epoxy molding

compound, is the weakest position of all adhesive

interface, and makes the delamination occurring and

spreading under the stress of thermal and humidity.

If the delamination occurs between EMC and chip, it

will cause an increase in the bonding wire resistance

as well as leakage current and decrease in

breakdown voltage even turn to open-circuit due to

mechanical tensile damage, also the passivating

layer are destroyed, which provides an easier

channel for the moisture immersing into the chip

surface and lead to the metal layer corrosion; While

if the delamination occurs between EMC and copper

substrate or lead frame, it will lead to Popcorn

Effect, while provides an channel for the moisture

immersing. In conclusion, once the delamination

occurs between EMC and other material, even if the

area is small, it will become the source of

delamination, and gradually expand in the actual

usage by thermal stress or mechanical stress until it

fails (PoPeom, 1995; Sheng Nian, 2014). The table

below shows the failure analysis of PEM in main

operating stress.

Table 1. The analysis of PEM in main operating stress.

No. Failure Mode

Failure

Mechanism

Die crack,

die adhesive failure

Temperature

stress

leakage current increased,

PN junction damaged

Thermal-

electric stress

Migration intermetallic

compound, Ohmic contact

degradation

Thermal

stress

4 Delamination

Humid-

thermo stress

3 RELIABILITY EVALUATION

OF OVER-TEMPERATURE

USING OF PEM

3.1 Select the Test Methods

Based on the analysis above, as well as combining

with GJB 7400-2011 “General specification for

semiconductor integrated circuits of qualitied

manufacturer certification” (G. Eason, et.al, 1955),

which is used to qualify the PEM used in military,

the high temperature storage, HAST, Temperature

cycle, and Steady state life test which are chosen to

qualify the reliability of PEM. Besides, the external

visual inspection, electrical performance test in room

temperature and Scanning Acoustic Microscope

(SAM) test are conducted after each test.

Meanwhile, in order to verify whether the different

temperature have different impact in structure and

performance for PEM, comparative tests are also

carried out.

3.2 Select the Test PEMs

This paper selects PEM ADV7123KSTZ140 as the

test sample. The maximum operating temperature

specified in the device manual is 85°C, but it is

tested the maximum operating temperature in actual

use is 115°C.

In order to verify whether the device at 85°C and

115°C temperature stress have the different impacts

on the performance and structure, 20 fully qualified

devices are selected to test under the manual

regulation temperature stress 85°C, marked as 1-1;

20 fully qualified devices are selected to test under

the actual temperature stress 115°C, marked as 2-1;

20 fully qualified devices with delamination

(without pins) at the lead frame are selected to test

under the manual regulation temperature stress

85°C, marked as 1-2; 20 fully qualified devices with

delamination (without pins) at the lead frame are

selected to test under the actual temperature stress

115°C, marked as 2-2. The devices information and

the test method are shown in table 2.

3.3 Process of the Tests

3.3.1 High Temperature Storage

After the high-temperature storage test for 48hours,

it is found that the functional performance

parameters of these 4 groups do not change too

much, and the delamination area of the 1-2 and 2-2

Research on Over-Temperature using of PEM Evaluation Method in Military

409

groups do not expand obviously, while there is no

obvious change of the 1-1 and 2-1 groups, which

indicates that different high-temperature storage had

little impact on the PEMs, and the typical test results

are shown in figure 1.

Table 2. The devices information and the test method.

No. Items

Test

condition of

1-1, 1-2

Test condition

of 2-1, 2-2

High

temperature

storage

85,48h 115,48h

2 HAST

85%RH/85,

1000h

85%RH/115,

1000h

Temperature

cycle

-40~85，

500 times

-40~115，

500 times

Steady state

life test

1000h, 85 1000h, 115

Devices information

No.

External

visual

inspection

Electronic

performance

SAM

1-1

2-1

qualified qualified qualified

1-2

2-2

qualified qualified

Defective but

not rejected

(a) Qualified (b) Defective but not rejected

Figure 1. SAM after high-temperature storage.

3.3.2 High Accelerated Stress Temperature

The second test is High accelerated stress

temperature (HAST), it is found that the functional

performance parameters of these 4 groups do not

change too much, still qualified. Group 1-1 and

group 2-1 have no obvious defects such as cavities

and cracks arise. Meanwhile the delamination area

of groups 1-2 and 2-2 increased, but groups 1-2 was

slightly less than that of groups 2-2. It can be

inferred that HAST can makes the delamination area

expansion. However, the expansion is related to

temperature: with the same humidity, the higher the

temperature, the larger the delamination area, while

the lower the temperature, the smaller the

delamination area (Xiao haihong, 2009), and the

typical test results are shown in figure 2 and figure

(a) Global photo of SAM (b) partial enlarged detail

Figure 2. SAM of group 1-2 after HAST.

(a) Global photo of SAM (b) partial enlarged detail

Figure 3. SAM of group 2-2 after HAST.

3.3.3 Temperature Cycle

The third test is temperature cycle. It is found that

the functional performance parameters of these 4

groups were still qualified, like it after HAST.

Group 1-1 and group 2-1 have no obvious defects

such as cavities and cracks arise. Meanwhile the

delamination area of groups 1-2 and 2-2 increased

than the area after HAST, and the functional

performance of these 2 groups are abnormal, and the

typical inspection results are shown in figure 4. That

is because the temperature change rate of

temperature cycle is large, and the rapid temperature

gradient will make the thermal stress increase which

makes the failure rate increase.

(a) Group 1-1, 2-1 (b) group 2-1, 2-2

Figure 4. SAM after temperature cycles.

Delamination part

ICVMEE 2019 - 5th International Conference on Vehicle, Mechanical and Electrical Engineering

410

Though the SEM examination for the group1-2

and group 2-2 which have the abnormal functional

performance, it is found that as the bonding line is

embedded in the packaging material and passes

through the bonding layer, the stress on the bonding

line will increase rapidly when the bonding layer

fails. The mismatch of thermal expansion coefficient

will result in repeated stress on the bonding line at

the interface with fatigue fracture. In the early stage,

crack initiate at stress point due to the repeated

action, and the stratification distance becomes

larger, the contact area becomes smaller or even

disconnects, resulting in parameter deviation or open

circuit at the low temperature. After the temperature

return to room temperature, the size of the

delamination decreases, the contact at the crack of

the bonding line resumes the connection, and the

electrical properties and functions return to normal.

If the bonding line crosses the delaminated interface,

it will cause fatigue fracture of the bonding line

under the action of thermal stress, which will

obviously increase the area of the disposed layer of

the lead frame with abnormal function and

performance of the PEMs (Driel, W.D.V, 2005).

Typical detection results are shown in figure 5.

(a) Global photo of SEM (b) partial enlarged detail

Figure 5. SEM of group 2-1 and 2-2 after Temperature

cycle.

3.3.4 Steady-State Life

The remaining two groups (groups 1-1 and 2-1)

were tested at 1000h, 85h and 1000h and 110

steady-state life. It is found that the group 1-1 is

functionally qualified at 1000h and 85°C, also

without any delamination inner the devices; but the

leakage current degradation of 2-1 was significantly

greater than that of the group 1-1, as shown in figure

Figure 6. Typical inspection results of leakage current.

Though the SEM examination for the group 1-1

and group 2-1, It is found that the gate oxide

thickness of group 2-1 is about 5nm, much less than

the gate oxide thickness of group 2-1, about 10nm,

that is because the lattice under high temperature is

unstable and the interface state of oxide layer

increases, resulting in the reduction of the thickness

of the gate oxide layer. through the thick oxide

breakdown voltage is (1.4~3)×107V/cm, eigen

breakdown voltage of oxide layer is (8~10)×106

V/cm. In general, under the action of electric

pressure, thin gate oxide layer is more likely to

cause breakdown, accompanied by thermal carrier

effect (TEVEROVSKY A, 2003). Typical inspection

results are shown in figure 7.

(a) Global photo of SEM (b) partial enlarged detail

Figure 7. Thickness of group 2-1 and 2-2 after Steady-

state life test.

3.3.5 Comparative Tests

The comparative tests are conducted in order to

verify whether the different temperature have

different impact in structure and performance for

PEM. We choose 5 devices from the group 2-1 after

steady-state life, and 5 new and qualified devices as

the comparative ones. According to GJB 4027A-

2006, method 1100, the external inspection, X-ray

inspection, SAM, internal inspection and SEM are

carried on by sequence, it is found that there is no

obvious difference between these 2 groups, which

means the tests for group 2-1 do not cause other

potential damage to the devices.

10 nm

Si substrate

AlAs

GaAs

Research on Over-Temperature using of PEM Evaluation Method in Military

411

4 CLOUSION

For PEM with inherent defects, they have poor

environmental adaptability, are more easily to fail

and have lower reliability in usage under

overtemperature conditions. This is because the

mismatch of thermal expansion coefficient can cause

stress at the interface between chip and package. The

temperature gradient caused by rapid temperature

change will increase the stress and accelerate the

failure rate. If the bonding line crosses the layered

interface, it will cause fatigue fracture of the

bonding line and abnormal function and

performance of the device under the action of a wide

range of temperature stress. It can be seen from the

results of tests in this paper, that HAST, temperature

cycle, and steady life test in actual usage

temperature can lead to device failure, inherent

defects effectively eliminate and encapsulation

device used in over temperature potential failure

under the application, evaluation device

environment adaptability; However, under the

condition of high-temperature storage, the device

can only bear high-temperature stress, and the

absence of a temperature gradient prevents the

device from potentially failing. And the temperature

cycle, HAST and steady life test in actual

temperature do not cause other potential damage to

the devices.

The research results in this paper can effectively

ensure the quality and reliability of devices over-

temperature using, and provide a theoretical basis

for the detection, evaluation, screening and failure

analysis for the PEMs used in over temperature.

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