DE102020112333A1 - Process for aging an electronic assembly, evaluation process for evaluating the durability of electronic assemblies and electronic assemblies - Google Patents

Abstract

The invention relates to a method for aging an electronic assembly (16) which has the following method steps: a. Cooling the assembly (16); b. Maintaining the cooling temperature for a period of time; c. Sudden heating of the assembly (16); andd. Maintaining the heating temperature for a period of time; unde. Repeat steps a) to d) until at least one damage occurs to the assembly (16). The invention also relates to an evaluation method for evaluating the durability of electronic assemblies (16) and an electronic assembly (16).

Description

The invention relates to a method for aging an electronic assembly. The invention also relates to an evaluation method for evaluating the durability of electronic assemblies and an electronic assembly.

In vehicle construction, electronic assemblies are increasingly used in components, such as in engine control, in driver assistance systems or in electric pumps, such as in electric coolant pumps. High demands are placed on these electronic assemblies in terms of robustness, temperature resistance, vibration resistance and reliability.

Electronic assemblies include electrical components, such as, for example, resistors, capacitors, transistors, diodes, coils and integrated circuits, which are connected to the electronic assembly, for example via solder connections on a printed circuit board.

While driving, the electronic assemblies can be subjected to different loads, such as mechanical and / or thermal alternating loads, which can lead to settling behavior in the soldered connections, to creeping of the soldered connections and to a change in the metal structure and ultimately to failure of the electronic assembly . In the case of electronic assemblies, there is usually a change in the material structure as a result of alternating thermal loads.

Since a change in the material structure only occurs over time and this time is not available during development and production, a so-called rape test in the form of a temperature shock test is used to assess the durability of electronic assemblies, which accelerates the aging of the electronic assembly and thus causes an accelerated change in the metal structure of the solder joint.

In the temperature shock test, the electronic assembly is cyclically exposed to temperature changes, with a change in the material structure due to the occurrence of mechanical thermal stress gradients. As a result, a statement can be made about the failure rate and thus the durability of an electronic assembly due to alternating thermal loads in a shorter time.

the end EP 0 203 348 B1 is a thermal shock test in which a sample is first immersed in a liquid made of perfluoropolyether with a temperature between -75 ° C and -55 ° C and after removing the sample, the same is immersed in a liquid made of perfluoropolyether with a temperature between 125 ° C and Submerged at 210 ° C. This process is repeated 20 to 40 times, the holding time of the sample per cycle in one of the liquids being between 30 seconds and 5 minutes.

the end DE 10 2016 207 527 A1 discloses a method for detecting the state of a connection between two or more components that together form a structural unit through thermal loads. In the process, a defined heat flow is fed into one of the sub-assemblies of a new unit or one that has been rated as good, then the resulting temperature profile over time is measured at the feed point or another defined point on the unit, and the thermal resistance of the joint is determined from the resulting Determined temperature profile. The above steps are then repeated with the structural unit to be assessed, and finally the thermal resistances of the joints for new or good parts are compared with the structural unit to be assessed.

The present invention is based on the object of a method for aging electronic assemblies that can be used both in development and in the production process and also enables electronic assemblies to be reliably aged. Furthermore, the invention is based on the object of creating an evaluation method for evaluating the durability of electronic assemblies and an electronic assembly with which process-related changes to the construction and connection technology of electronic assemblies can be recognized.

To achieve the object, a method with the features of claim 1, an evaluation method with the features of claim 7 and an electronic assembly with the features of claim 13 are proposed.

Advantageous refinements of the method are the subject matter of the respective dependent claims.

According to a first aspect, a method for aging an electronic assembly is proposed, which has the following method steps. First, the assembly is cooled down and, in a second step, the cooling temperature is maintained over a period of time. The assembly is then suddenly heated in a third step. In a fourth step, the heating temperature is maintained over a period of time. The steps of cooling down, maintaining the cooling temperature, heating and maintaining the heating temperature are repeated until at least one damage occurs to the assembly.

The method for aging an electronic assembly creates an accelerated qualitative test method for aging an electronic assembly, which can be used both in the development process of the electronic assembly and in the downstream production process of the electronic assembly. By repeating the cooling, maintaining the cooling temperature, heating and maintaining the heating temperature, the assemblies are subjected to cyclical thermal stress, which leads to accelerated aging of the electronic assembly. This allows weak points and design errors to be discovered reliably and at an early stage.

The present method can also be referred to as a rush test for the aging of electronic assemblies or as a thermal shock cycle or method for the aging of electronic assemblies.

In an advantageous embodiment, the assembly is thermally stressed until damage to at least one soldered connection of the electronic assembly or a change in the metal structure of the soldered connection occurs. In the present case, damage is understood to mean a significant previous degree of damage to the assembly and connection technology of the electronic assemblies or a failure of the electronic assemblies. As a result of the damage, the solder connection settles and / or the metal structure of the solder connection changes, so that the electronic assembly no longer functions properly.

With the method, a large number of electronic assemblies can advantageously be aged at the same time.

In the present case, an electronic assembly is a functional unit of electrical components or elements, such as resistors, capacitors, transistors, diodes, coils and / or integrated circuits, which are connected to the electronic assembly on a printed circuit board by means of at least one solder connection and / or several solder connections be understood. In the present case, damage to the assembly is understood to mean the state in which the solder connection shows a setting behavior and the metal structure of the solder connection changes. In the present case, the assembly can also be referred to as an electronics assembly.

In an advantageous embodiment, the holding time of the cooling temperature and / or the heating temperature depends on the material used for the solder connection and also on the requirements for the structural change in the solder connection.

In an advantageous embodiment, the thermal stress takes place in a temperature change chamber.

In an advantageous embodiment, the cooling, holding and heating are repeated up to 1500 times. This ensures that the assembly is subjected to aging to reveal weak points and design flaws.

In an advantageous embodiment, the assembly is cooled down to -50 ° C. This corresponds to a low temperature in the subpolar climatic zone.

In an advantageous embodiment, the assembly is suddenly heated to at least 100 ° C. This corresponds to a temperature in the tropical climate zone when the vehicle is exposed to the sun. Advantageously, the assembly can be suddenly heated to more than 100 ° C.

In an advantageous embodiment, the holding time for the cooling temperature and / or the heating temperature is between 1 min and 2 hours. The holding time for the cooling temperature and / or the heating temperature is also advantageously between 5 minutes and 30 minutes. The holding time is preferably 10 minutes. The holding time for the cooling temperature and / or the heating temperature depends on the material used for the solder connection and also on the requirements the structural change of the solder connection.

In an advantageous embodiment, the cooling, the maintenance of the cooling temperature, the heating and the maintenance of the thermal temperature are carried out until the assemblies fail. This means that the assembly is thermally stressed until the solder connections fail. In contrast to the damage to the assembly, the assembly is thus thermally stressed in such a way that at least one solder connection is completely destroyed and the electronic assembly no longer functions.

According to a further aspect, an evaluation method for evaluating the durability or failure rate of electronic assemblies is proposed, which has the following method steps: First, reference assemblies are provided from a set of validated assemblies. The reference assemblies are then subjected to cyclical thermal loads until the reference assemblies are damaged. For this purpose, the assemblies are cooled down and, in a second step, the cooling temperature is maintained over a period of time. The assemblies are then suddenly heated. The steps of cooling, maintaining the cooling temperature, heating and holding the heating temperature are repeated until damage occurs to the assemblies. Thereafter, the number of cycles up to the occurrence of the damage to the reference modules is determined, and an average reference number of cycles is calculated on the basis of the determined number of cycles, or the reference modules are dynamically stressed until they fail. Subsequently, assemblies are taken from a set of assemblies to be tested. These assemblies are subjected to cyclical thermal loads until the reference assemblies are damaged. For this purpose, the assemblies are cooled down and, in a second step, the cooling temperature is maintained over a period of time. The assemblies are then suddenly heated. The steps of cooling down, maintaining the cooling temperature, heating and maintaining the heating temperature are repeated until damage occurs to the assemblies. The number of cycles up to the occurrence of damage to the assemblies is then determined, and an average number of cycles is calculated on the basis of the number of cycles determined, or the assemblies are dynamically stressed until they fail. Finally, the mean number of cycles is compared with the mean number of reference cycles, or the duration until the failure of the reference modules is compared with the duration until the failure of the modules.

The assessment procedure creates an accelerated qualitative test procedure for determining the durability or failure rate of electronic assemblies, with which process-related changes to the structure and connection technology of electronic assemblies can be reliably detected. In addition, the evaluation method can be used both during the development of the electronic assemblies and in the downstream production process of the electronic assemblies or the process of installing the electronic assemblies in a component or a system. This means that quality risks can be detected early and field failures avoided.

The variant in which the modules are only subjected to thermal stress and the average number of cycles until damage occurs is the less expensive variant compared to the variant in which the modules are additionally exposed to dynamic stress. The variant in which the assemblies are exposed to dynamic stress has the advantage that it is more clearly worked out which part or which components of the assemblies are particularly stressed.

If, when comparing the mean number of cycles with the mean reference number of cycles, there is a discrepancy, in particular a significant discrepancy, it can be assumed that the component properties have changed, which is to be assessed with regard to the component quality.

In the case of the validated assemblies, it has already been proven that they are OK or in good condition. The validated assemblies can therefore also be referred to as good parts.

The assemblies, in particular the electronic assemblies, can be resistors, capacitors, transistors, diodes, coils and / or integrated circuits that are connected to the electronic assembly on a printed circuit board by means of solder connections.

The assemblies in step b) and e) are preferably subjected to cyclical thermal loads until at least one damage occurs on each assembly. In the variant in which the mean reference number of cycles is determined, the assemblies in steps b) and e) are advantageously subjected to cyclical thermal stresses until they fail. In the variant in which the assemblies are dynamically stressed, the assemblies in steps b) and e) are furthermore advantageously subjected to cyclical thermal stresses up to a significant previous degree of damage. In an advantageous embodiment, the reference assemblies and the assemblies are loaded with vibrations in the event of dynamic loading. The assemblies are advantageously loaded with assembly-specific oscillations or vibrations, in particular with an assembly-specific oscillation or vibration profile.

In an advantageous embodiment, the duration and / or the amplitude of the failed assemblies are compared with the amplitude and / or the duration of the failed reference assemblies.

In an advantageous embodiment, each reference assembly and each assembly are integrated into a component or a system network in order to carry out the dynamic loading. This means that the reference assemblies or assemblies are combined with further parts and / or assemblies to form a component and / or are connected with further parts, assemblies and components to form a system, and these components are dynamically stressed. One component can be an electric coolant pump or an electric motor. A system network can be, for example, a drive unit including assembly elements.

In an advantageous embodiment, the critical frequency positions for performing the Dynamic stress is determined by simulation on component level and / or on system network level of each reference assembly and each assembly. The simulation is advantageously carried out by means of FEM simulation, in particular by means of FEA simulation. The critical frequency positions are also advantageously determined by modal analysis. In an advantageous embodiment, this takes place in parallel to steps b) and e).

In an advantageous embodiment, the dynamic loading is carried out in a vibration device. The vibration device can be a shaker on which the components with the integrated electronic assemblies or the system network with the integrated electronic assemblies are exposed to vibrations. On the shaker, the components or the system group are loaded with the component-specific or system group-specific vibration profile determined by simulation.

In an advantageous embodiment, steps d) to g) are repeated at regular time intervals. This means that assemblies are removed from a set of assemblies to be tested at regular time intervals, these are cyclically stressed by temperature changes until the solder connections are damaged, then an average number of cycles is calculated on the basis of the number of cycles determined until the damage occurs, and finally the number of cycles is calculated first The mean number of reference cycles determined is compared with the mean number of cycles or the modules are subjected to dynamic loads until they fail. The regular intervals are advantageously between approx. 3 months and approx. 6 months.

In an advantageous embodiment, the mean number of reference cycles and the mean number of cycles are determined on a statistically relevant random sample of damaged, in particular failed reference assemblies and damaged, in particular failed, assemblies.

According to a further aspect, an electronic assembly is proposed which is tested with the evaluation method for evaluating the durability or failure rate of electronic assemblies.

• 1 eine schematische Darstellung eines Ablaufs eines Bewertungsverfahrens gemäß einer ersten Variante; und
• 2 eine schematische Darstellung eines Ablaufs des Bewertungsverfahrens gemäß einer zweiten Variante.

A method, an evaluation method, an electronic assembly and further features and advantages are described in more detail below on the basis of exemplary embodiments which are shown schematically in the figures. Here show:

• 1 a schematic representation of a sequence of an evaluation method according to a first variant; and
• 2 a schematic representation of a sequence of the evaluation method according to a second variant.

This in 1 The evaluation method shown serves to evaluate the durability or failure rate of electronic assemblies, which is described below, in which a method for accelerated aging of the electronic assemblies is used to evaluate the durability.

In a first step S1 of the evaluation method according to the first variant, reference assemblies are used 10 from a number of validated electronic assemblies 12th taken.

In a second step S2 of the evaluation method according to the first variant, the method for aging the reference assemblies is used 12th used. For this purpose, the removed reference assemblies are used 10 in a temperature change chamber 14th cyclically stressed by temperature changes until a failure at the soldered connections of the reference modules 10 occurs. In the aging process, the reference assemblies 10 The reference modules are cooled down to -50 ° C cyclically up to 1500 times and after a holding time at -50 ° C has elapsed 10 suddenly heated to 100 ° C or more and held. After the hold time has elapsed, the reference modules are cooled down to -50 ° C and a new cycle begins. The holding time at -50 ° C. and / or at 100 ° C. or more is at least 10 minutes, since solder joints in particular exhibit setting behavior and the metal structure changes.

In a third step S3 of the evaluation method according to the first variant, the number of cycles until the failure occurs on the reference modules 10 determined, and on the basis of the determined number of cycles, a mean reference number of cycles is determined using a statistically relevant sample.

In a fourth step S4 of the evaluation method according to the first variant, electronic assemblies 16 from a number of assemblies to be tested 18th which, for example, come from ongoing production.

In a fifth step S5 of the evaluation method according to the first variant, the method for aging the assemblies is used again 16 used. For this purpose the assemblies 16 cyclically stressed by temperature change until a failure at the soldered connections of the assemblies 16 occurs. In the process of aging, assemblies 16 The modules are cyclically cooled down to -50 ° C up to 1500 times and after a holding time at -50 ° C has elapsed 16 Suddenly heated to at least 100 ° C and held. After the hold time has elapsed, the reference modules are cooled down to -50 ° C and a new cycle begins. The holding time at -50 ° C. and / or at 100 ° C. or more is at least 10 minutes, since solder joints in particular exhibit setting behavior and the metal structure changes.

In a sixth step S6 of the evaluation method according to the first variant, the number of cycles until the failure occurs on the assemblies 16 determined, and on the basis of the determined number of cycles, an average number of cycles is determined using a statistically relevant sample.

In a seventh step S7 of the evaluation method according to the first variant, the mean number of cycles is compared with the mean reference number of cycles, with significant deviations from the reference number of cycles being assumed that the component properties have changed, which is to be evaluated with regard to the component quality.

Steps S4 to S7 are repeated at regular intervals, that is, every 3 months to 6 months, and the result is compared with a reference group in order to identify process-related changes to the structure and connection technology of the electronic assemblies during the ongoing production process 16 to recognize.

In 2 a second variant of the evaluation method is shown, which is described below, the same reference numerals being used for identical or functionally identical parts.

In a first step S1 of the evaluation method according to the second variant, reference assemblies are used 10 from a number of validated electronic assemblies 12th taken.

In a second step S2 of the evaluation method according to the second variant, the method for aging the reference assemblies is used 12th used. For this purpose, the removed reference assemblies are used 10 in a temperature change chamber 14th cyclically stressed by temperature changes. In contrast to the first variant, the reference assemblies are 12th not aged to the point of failure of the solder connections, but only to a significant degree of damage. In the aging process, the reference assemblies 10 The reference modules are cooled down to -50 ° C cyclically up to 1500 times and after a holding time at -50 ° C has elapsed 10 Suddenly heated to at least 100 ° C and held. After the hold time has elapsed, the reference modules are cooled down to -50 ° C and a new cycle begins. The holding time at -50 ° C. and / or at 100 ° C. or more is at least 10 minutes, since solder joints in particular exhibit setting behavior and the metal structure changes.

In parallel with the aging in step S2, critical frequency positions are determined by simulation, in particular FEM simulation at the component level and / or in the system network. For this purpose, a reference module is created for each simulation 10 in one component 20th integrated and exposed to oscillations or vibrations via simulation in order to determine the critical component-specific vibration profile. The critical frequency positions can be determined using modal analysis.

In a third step S3 of the evaluation method according to the second variant, a pre-aged reference module is used in each case 10 in one component 20th integrated, and the component 20th is on a vibrating device 22nd with the frequencies determined as critical mechanically, in particular dynamically, applied until the soldered connections of the reference assemblies 10 fail.

In a fourth step S4 of the evaluation method according to the second variant, assemblies 16 from a number of electronic assemblies to be tested 18th taken.

In a fifth step S5 of the evaluation method according to the second variant, the method for aging the assemblies 16 used. For this purpose, the removed assemblies 16 in a temperature change chamber 14th cyclically stressed by temperature changes. In contrast to the first variant, the assemblies are 16 not aged to the point of failure of the solder connections, but only to a significant degree of damage. In the process of aging, the assemblies are 16 The assemblies are cyclically cooled down to -50 ° C 1500 times and after a holding time at -50 ° C 16 Suddenly heated to 100 ° C and held. After the hold time has elapsed, the reference modules are cooled down to -50 ° C and a new cycle begins. The holding time at -50 ° C. and / or at 100 ° C. or more is at least 10 minutes, since solder joints in particular exhibit setting behavior and the metal structure changes.

In parallel with the aging in step S5, critical frequency positions are determined by simulation, in particular FEM simulation at the component level and / or in the system network. For this purpose, one module is created for each simulation 16 in one component 20th integrated and simulated vibrations or exposed to vibrations in order to determine the critical component-specific vibration profile. The critical frequency positions can be determined using modal analysis.

In a sixth step S6 of the evaluation method according to the second variant, a pre-aged assembly is recorded 16 in one component 20th integrated, and the component 20th is on a vibrating device 22nd with the frequencies determined as critical mechanically, in particular dynamically, applied until the soldered connections of the assemblies 16 fail.

In a seventh step S7 of the evaluation method according to the second variant, the duration and / or the amplitudes of the reference assemblies are determined 10 with those of the assemblies 16 compared, whereby in the case of significant deviations in amplitude and / or duration it can be assumed that the component properties have changed, which is to be assessed with regard to the component quality.

Steps S4 to S7 are repeated at regular intervals, that is, every 3 months to 6 months, and the result is compared with a reference group in order to identify process-related changes to the structure and connection technology of the electronic assemblies during the ongoing production process 16 to recognize.

Variant 1 is the less expensive variant compared to variant 2. Variant 2 has the advantage that it is more clearly worked out which part or which components of the assemblies 16 are particularly burdened.

The evaluation procedure creates an accelerated qualitative test procedure to determine the durability or failure rate of electronic assemblies 16 , with which process-related changes to the structure and connection technology of electronic assemblies can be reliably detected. This means that quality risks can be detected early and field failures avoided. The aging process used here creates an accelerated qualitative test process for the aging of an electronic assembly 16 that both in the development process of the electronic assembly 16 as well as in the downstream production process of the electronic assembly 16 can be used.

List of reference symbols

10

Reference assembly

12th

validated assemblies

14th

Temperature change chamber

16

module

18th

assembly to be tested

20th

component

22nd

Vibration device

QUOTES INCLUDED IN THE DESCRIPTION

This list of the documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent literature cited

• EP 0203348 B1 [0007]
• DE 102016207527 A1 [0008]

Claims (13)

A method for aging an electronic assembly (16), comprising the following method steps: a. Cooling the assembly (16); b. Maintaining the cooling temperature for a period of time; c. Sudden heating of the assembly (16); and d. Maintaining the heating temperature for a period of time; and e. Repeat steps a) to d) until at least one damage occurs to the assembly (16). Procedure according to Claim 1 , characterized in that steps a) to c) are repeated up to 1500 times. Procedure according to Claim 1 or 2 , characterized in that the assembly (16) is cooled down to -50 ° C. Method according to one of the preceding claims, characterized in that the assembly is suddenly heated to at least 100 ° C. Method according to one of the preceding claims, characterized in that the holding time in step b) and / or d) is between approx. 1 min and approx. 2 h. Method according to one of the preceding claims, characterized in that steps a) to c) are carried out until the assembly (16) fails. Evaluation method for evaluating the durability of electronic assemblies (16), which has the following method steps: a. Providing reference assemblies (10) from a set of validated assemblies (12); b. Cyclical thermal loading of the reference assemblies (10) according to the method according to one of the Claims 1 until 6th ; c. Determination of the number of cycles up to the occurrence of damage to the reference assemblies (10) and determination of an average reference number of cycles on the basis of the determined number of cycles, or dynamic loading of the reference assemblies (10) up to their failure; d. Removing assemblies (16) from a set of assemblies (18) to be tested; e. Cyclic thermal loading of the assemblies (10) according to the method according to one of the Claims 1 until 6th ; f. determination of the number of cycles up to the occurrence of damage to the assemblies (16) and determination of an average number of cycles on the basis of the determined number of cycles, or dynamic loading of the assemblies (16) up to their failure; G. Comparison of the mean number of cycles with the mean reference number of cycles or comparison of the time until the failure of the reference modules (10) with the time until the failure of the modules (16). Evaluation procedure according to Claim 7 , characterized in that each reference assembly (10) and each assembly (16) are integrated in a component (20) or a system network in order to carry out the dynamic loading. Evaluation procedure according to Claim 7 or 8th that the critical frequency positions for performing the dynamic loading are determined by simulation on the component level and / or on the system network level of each reference assembly (10) and each assembly (16). Evaluation procedure according to one of the Claims 7 until 9 , characterized in that the dynamic loading is carried out on a vibration device (22). Evaluation procedure according to one of the Claims 7 until 10 , characterized in that steps d) to g) are repeated at regular time intervals. Evaluation procedure according to one of the Claims 7 until 11 , characterized in that the mean reference number of cycles and the mean number of cycles are determined on a statistically relevant sample of damaged reference assemblies (10) and damaged assemblies (16). Electronic assembly (16) evaluated with an evaluation method according to one of the Claims 7 until 12th .

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