DE102009012296A1 - Method for monitoring the temperature-time load of at least one component on a printed circuit board, a corresponding temperature-time indicator and its application - Google Patents

Abstract

The invention relates to a method for monitoring the temperature-time load of at least one component (3) on a printed circuit board (2) by means of an irreversible color-reversing time-temperature indicator (TTIs) (6), characterized in that after the assembly and Soldering of the component (3) at least one TTI control element (6) on a predetermined surface with a certain distance to the monitoring component (3) is applied and TTI control element (6) TTI substances from organic or inorganic salts of transition metals with a molecular decomposition process and homogeneously dispersed in a polymeric matrix with activation in each relevant temperature range are used and these TTI substances (6) have an irreversible visually or machine verifiable color change in the relevant temperature range and depending on the duration of operation in the relevant temperature range and so the temperature Rbelastung a component (3) on a printed circuit board (2) can be monitored. A corresponding temperature-time indicator (TTI) (6) and its application is also described.

Description

Introduction and problem definition:

The The invention describes methods for monitoring the temperature-time load at least one component on a printed circuit board, a display device for the traceability of life-reducing overheating of electronic components on support parts with each other connected electrical contacts.

a concrete problem case represents thereby, by the possibility the direct electrical control of LEDs and a thereby resulting electrical overload control following overheating these LEDs.

LEDs have advantages over conventional ones everywhere Light sources where their shorter life increased Costs or safety risks, or where the energy use is particularly relevant. The current application fields are the same far as unlimited. Currently a big market ship and aviation; so they become with navigation lights, Warning lights and airfield lights just because of the long life especially in terms of safety and low maintenance intervals used advantageously. Also in traffic safety are many conventional light sources in use, replaced by LED sources can be. Here is above all the cost savings through more than 90% lower electrical power consumption in the foreground. In analytical metrology as well as in medical technology also used LEDs. For the latter applications Above all, the achievable color mixtures and the low heat development of great advantage. Lately, LEDs are also in increasingly used in the automotive industry. So be already rear, warning but also front lights equipped with LEDs, as they are in terms of energy efficiency and design options consistently superior to the conventional light bulb are.

Around To realize applications with LEDs with high brightness especially high performance LEDs with operating power over 1 watt used. By bigger chips and higher Current densities will in the future be the operating per LED continue to increase.

A another way to increase the radiant power, is the merging of several LEDs into an array. One of the most important Design parameters for today's powerful LED arrays is the distance of the individual chips. Dense packing brings the following Advantages: Increasing the specific light emission, more efficient Use of beam-shaping optics, enabling more compact Designs and reduction of system costs.

at the increase in power densities of each chip and when reducing the distances in an array between the But chips must be taken care of at the same time the accordingly also increased heat loss is dissipated to ensure that the heat generated is sufficiently diverted away from the semiconductor chip.

A too much warming of the LEDs during the In fact, operation can be detrimental or even lead to the destruction of the component. For this Reason must be ensured during the operation of the LED be that the temperature at the barrier layer (active zone) of the p-n transition a certain critical temperature - for example 125 ° C - not exceeding (For an AlInGaP / AlGaAs chip for Example, the colors near infrared (NIR) and cherry red to Green-yellow can produce, the temperature of the junction should be Do not exceed 85 ° C). A higher one Temperature leads to the degradation of the barrier layer, which initially changed the color characteristics of the component. As higher temperatures in the barrier layer increase the lifetime shorten the component, it comes at a longer Operation at higher temperatures for destruction the barrier layer and thus the total failure of the component.

These Danger results from the fact that only part of the LED recorded electrical power is converted into light while the remaining part is converted into heat. The operating parameters of LEDs are therefore dependent on the type of mounting, to choose the installation and ambient conditions in such a way for example, the junction temperature of the LED is 125 ° C does not exceed.

Out It is known in the prior art that LEDs on support parts be mounted and contacted used. Usually These consist of a glass fiber reinforced epoxy resin system, however, having a high thermal resistance and thus the derivation of the heat loss from the LED difficult.

alternative are also known ceramic plates, although better thermal properties offer, but are very brittle and fragile, which severely restricts their use as a carrier material.

In high performance technical applications are made in accordance with the The prior art also used metal core circuit boards. These consist of a metal base, an insulating layer and a Interconnect level.

Furthermore, copper plated vias or metal plates, which under the component one ensure better heat dissipation. Despite all these possibilities, it may be by operating the component at high operating parameters for extended periods of time to z. As to increase the luminous efficacy, come to an increased heat development, so that the derivation of the heat loss produced by the substrate can not be guaranteed. It is therefore important that the component is operated in the parameters provided in order to avoid a time-defined overheating and thus the total failure of the component.

later At the moment, it is hardly possible to prove whether the component is actually failing by a z. B. too high drive current and thus by a thermal conditional destruction of the barrier was conditional.

Out This reason would be for the manufacturer of the component and the substrate an indication of whether the component is in operation within of the specified operating parameters was of the utmost importance. This could result in recourse claims be effectively and objectively counteracted by the end customer. These recourse claims are in the face of high expectations Life of the components particularly explosive, since the components with it their, compared to conventional illuminants justify higher initial acquisition costs with.

Existing solutions:

There are approaches to solve the problem described above by indicators with waxes. Waxes react spontaneously in the event of a critical temperature violation and therefore can not guarantee a time-delayed color change (see, for example, US Pat. US 6,564,742 B2 ; US 7,030,041 B2 ).

The indicators are additionally elaborate in conventional construction (several layers by film, absorbent layer and wax) and large (about 10-15 mm in diameter) designed. This prevents application on many test specimens from the outset. Such wax indicators are for example in the US 7063041 B2 or the WO2007 / 012132A1 shown.

A simplified application of wax drops in the dispenser process still does not solve the problem of spontaneous handling, but even brings additional difficulties possible abrinner of the wax when melting, as soon as the DUT not completely horizontally installed is. This makes a traceability difficult again; However, contamination of surrounding components is the logical risk.

Also various additional wiring in the sense of overdrive protection ("Fuse") are neither cost effective to install still effectively visually verifiable.

task The present invention is the permanent, color traceability of temperature excesses ('check point') of the test object (this is due to excessive electrical controls to conditions), which lead to a massive reduction in life; and thus non-verifiable recourse claims towards the manufacturer.

The Solution of the task is done by the technical Teaching of claim 1.

essential A feature of the invention is the arrangement of one or more easy to apply control points (defined amount of a substance), at a defined time-temperature curve a lasting, irreversible Leave a color impression on the test specimen. The order several control points can optionally be in addition to the time-temperature characteristic a control point additionally several time-temperature ranges cover (eg once at 80 ° C and about 4 days, another Time at 70 ° C and about 7 days). So it is in a time-temperature integrating display device

A whole essential requirement of these checkpoints is the up too, but not exclusively delayed color change from several hours to days. This will be a conventional solution of the problem about display of abrupt temperature violations avoided.

The relevant time-temperature characteristic is from manufacturer to manufacturer different, since different reference measuring points are used. In any case, the aim is to standardize the used ones Time-temperature-sensitive substances and exclusive Variation of the distance to the tested component (Degrading temperature profile over increase the spatial distance).

Important is in the sense of quality inspection in goods issue but also in the later review of the control point (s) that it is next to the untransformed Checkpoint also gives a converted checkpoint, the the functionality of the unchecked checkpoint ensures and in each exam a corresponding Certainty delivers.

• – Offsetdruck
• – Flexodruck
• – Rastertiefdruck
• – Tampondruck
• – Ink-Jet-Druck
• – Dispenser-Applikation
• – Rollen-Applikation
• – Rakel-Applikation
• – Streich-Applikation
• – Sprüh-Applikation

Our solution envisages the use of thermochromic substances which are applied to the test specimen in different processes can. However, among other things, not only the following procedures are provided:

• - offset printing
• - flexographic printing
• - Raster gravure
• - Pad printing
• - Ink-jet printing
• - Dispenser application
• - Roller application
• - Doctor application
• - Prank application
• - Spray application

• – Salze/Oxide mit Phasenübergang im relevanten Temperaturbereich
• – Salze mit Kristallwasserverlust im relevanten Temperaturbereich
• – oxidierbare Substanzen
• – Substanzen mit Schmelzpunkt im relevanten Temperaturbereich
• – Substanzen mit Zersetzung im relevanten Temperaturbereich
• – Mehrkomponentensysteme mit Aktivierung im relevanten Temperaturbereich

The substances may, however, not only be the following:

• - Salts / oxides with phase transition in the relevant temperature range
• - Salts with water loss in the relevant temperature range
• - oxidizable substances
• - substances with melting point in the relevant temperature range
• - Substances with decomposition in the relevant temperature range
• - Multi-component systems with activation in the relevant temperature range

In In all cases, it must be ensured that the Substances are recycled in accordance with environmental requirements.

The amount of application is tailored to the particular application and averaged but not generally about 3 to 20 picoliter. The space required for the checkpoint thus averages but is not generally about 1 to 9 mm ² .

• – Weiß auf Schwarz
• – Schwarz auf weiß
• – Blau auf rot
• – Blau auf grün
• – Blau auf transparent
• – Grün auf rot
• – Rot auf transparent

The color change is variable and can be designed differently for each time-temperature behavior. Thus, color envelopes are possible, which, however, not only have the following effects:

• - white on black
• - Black on white
• - Blue on red
• - Blue on green
• - Blue on transparent
• - Green on red
• - Red on transparent

Of the Subject of the present invention does not arise only from the subject matter of the individual claims, but also from the combination of the individual claims among themselves.

All in the documents, including the abstract Information and features, in particular the spatial shown in the drawings Training, are claimed as essential to the invention, as far as individually or in combination with the state of the art Technology is new. In the following, the invention will be described with reference to only one Design execution illustrative drawings closer explained. Here are the drawings and their Description further features essential to the invention and advantages of the invention.

It demonstrate:

1 : Schematically, the plan view of an unpopulated multiple-benefit printed circuit board consisting of a plurality of single-use printed circuit boards

2 : The top view of a populated single-use circuit board.

3 : Temperature profile on a display device according to the prior art

4 : Temperature profile on a display device according to the invention

5 : gradual color change at a checkpoint

6 : Representation of the time-integrated envelope of the checkpoint

In 1 is a schematic plan view of an unpopulated Mehrfachnutzenleiterplatte ( 1 ) consisting of a plurality of single-use printed circuit boards ( 2 ).

in the Present example will be a so-called one-sided aluminum core printed circuit board shown for the assembly of LED components.

The scribe lines ( 8th ) are usually already performed by the PCB manufacturer and serve to the multiple-benefit PCB ( 1 ) after the assembly and soldering process in populated single-use printed circuit boards ( 2 ) to separate.

In 2 is the top view of a populated single-use circuit board ( 2 ).

The contact pads ( 4 ) on the printed circuit board ( 2 ) serve the electrical contacting of a on the circuit board ( 2 ) arranged component ( 3 ). In the present case, the contact surfaces for contacting an LED ( 3 ), whereby the actual LED ( 3 ) is not visually recognizable due to the small size of an SMD (surface mount device) component.

In the present application of a thermally good dissipative aluminum core circuit board as Carrier for the component to be monitored ( 3 ) the surface ( 9 ) covered with a usually white solder mask. This reflects a stray LED light upwards.

To monitor the temperature-time load of the component, a TTI control element ( 6 ) are arranged on the circuit board.

The control measuring point ( 5 ) is designed with a black and well absorbing and non-reflective paint and is used for non-contact temperature measurement.

The checkpoint ( 7 ) serves the visual inspection of the TTI ( 6 ) and is executed in the same color as the TTI ( 6 ) when a predetermined, permitted temperature-time load of the component ( 3 ) reached.

In all cases, the distances of the elements ( 5 . 6 . 7 ) of the component ( 3 ) the indicator range of the TTI (or 6 ) to this distance and the maximum temperature-time capacity of the component ( 3 ).

The attachment of the TTI ( 6 ) is preferred after the assembly and soldering of the components ( 3 ) on the multiple-use circuit board ( 1 ) and before singling into populated single-use circuit boards ( 2 ) respectively.

In particular, several TTIs ( 6 ) to be ordered. Identically sensitive TTIs ( 6 ) and in this case the distance to the heat source ( 3 ) varies to indicate different high temperature-time loads. It can be shown visually such a course of the temperature-time load. It is also possible to use different sensitive TTIs ( 6 ) next to each other or at the same distance from the heat source ( 3 ), whereby also the height of the temperature-time load can be visually displayed.

The TTIs ( 6 ) can be further executed in almost any shape from round to oval to line-like or in the form of a number.

For example Temperature values can be as 60 ° C-70 ° C-80 ° C-90 ° C etc. are arranged and depending on the temperature-time load then color changes recognizable.

The temperature numbers or generally a description can also be in addition to the z. B. punctual TTIs ( 6 ) by surface printing. The printing process can be used with which the control measuring point ( 5 ) will be produced.

The attachment of TTIs ( 6 ) can be done by dispenser or pad printing or ink jet or spray nozzle or aerosol jet.

The sensitivity of TTIs ( 6 ) can also be varied by the applied layer thickness.

The TTI substance ( 6 ) is selected from organic or inorganic salts of transition metals with a molecular decomposition process and homogeneously dispersed in a polymeric matrix with activation in the relevant temperature range is formed and these TTI substances ( 6 ) have an irreversible visually or machine-verifiable color change in the relevant temperature range of about 30 ° C to 150 ° C, preferably in the range 60 ° C to 120 ° C and in dependence on the duration. In this way, the temperature-time load of a component ( 3 ) on a printed circuit board ( 2 ) are visually and / or mechanically monitored.

The temperature-time-indexing substance of the TTI element ( 6 ) Is exemplified of copper (II) hydroxide Cu (OH) _2, nickel (II) chloride hexahydrate NiCl ₂ · 6H ₂ O, Bishexamethylentetramin cobalt (II) nitrate decahydrate Co (NO _{3) 2} · 2C ₆ H ₁₂ N ₄ · 10H ₂ O or nickel (II) oxalate NiC ₂ O ₄ homogeneously dispersed formed in a polymeric matrix and applied by means of dispenser or pad printing or inkjet or spray nozzle or Aerosoljet.

The 3 shows a temperature profile with a color change according to the prior art. For example, waxes are used as indicator material. These react spontaneously in the event of a critical temperature violation and therefore can not guarantee a time-delayed color change.

This is in 3 shown. Reach the temperature curve 11 the critical temperature limit 10 at position 12 there is an irreversible color change 13 , It does not matter if the temperature is a short time later at position 14 falls below the critical limit and stays there for a certain time (position 15 ) or the temperature limit 10 again exceeds (position 16 ). How long a temperature exceeded and whether a limit for the pn junction of the LED limit was exceeded for a long time, can not be demonstrated in the prior art.

4 shows the course according to the invention of the monitoring of a component ( 3 in 2 .) The temperature profile to be monitored 11 begins below a monitored temperature limit 17 at z. B. 80 degrees Celsius.

At position 18 the temperature curve cuts this temperature limit 17 and gets into a surveillance area. It is important that a time-integrated capture of the TTI control element ( 6 ) temperature, so that a temperature exceeded in the period between the times t1 and t2 to the position 19 to a gradual color change of the TTI control element ( 6 ) leads. The more often and thus the longer the temperature limit 17 is exceeded, z. Between times t3 and t4 or t5 and t6, and / or the faster the temperature rise (at position 20 and / or the higher the temperature (position 21 ), the more intense is the color change of the TTI control element ( 6 ).

On this way will be an integrating measurement to generate a or several color changes, at the both the absolute height of the temperature and the Exposure time of this temperature recorded on the control point become.

The 5 shows the gradual course of the color change of a TTI control element 6 , which initially has a white color, for example, and as a TTI control element on further exposure to temperature 6 ' for example, a pink and then as a TTI control element 6 '' for example, an orange and then as a TTI control element 6 ''' For example, takes a magenta-red color.

The 6 shows the time integration. It can be seen that at position 22 first a pink color change of the TTI control element 6 ' done, to the position 23 stops. After that, the color of the TTI control element changes 6 ' into a TTI control element 6 '' with orange color and then - from position 24 to position 25 into a TTI control element 6 ''' with magenta-red coloring.

These Specifications apply at a constant temperature of, for example 120 degrees Celsius. However, the temperature rises to a higher Value, the color change happens faster. The width of the bars gets narrower then.

All the above designs can also provide that the heat conducting connection between the LED chip 3 and the control points 6 through inner layers of the circuit board 1 is generated, in which case at the place of attachment of the control points 3 . 4 a blind hole on the surface of the circuit board 1 appropriate, in each case a checkpoint 5 . 6 is arranged in heat-conducting connection with this inner heat-conducting layer. Such inner, thermally conductive layers having printed circuit boards usually have an inner metal core.

In all applications should have a good visual visibility of the control points 5 . 6 be given.

1

Multiple-board unpopulated

2

One-up board stocked

3

Component contact surfaces with component, for. B. LED or IC or passive components (= heat source)

4

contact surfaces (Pads) on the circuit board

5

Control measuring point

6

TTI Control element (temperature-time indicator)

7

control element or checkpoint

8th

scribe lines

9

PCB surface

10

temperature limit

11

temperature curve

12

position

13

color change

14

position

15

position

16

position

17

temperature limit

18

position

19

position

20

pitch

21

position

22

position

24

position

25

position

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• US 6564742 B2 [0015]
• US 7030041 B2 [0015]
• US 7063041 B2 [0016]
• WO 2007/012132 A1 [0016]

Claims (17)

Method for monitoring the temperature-time load of at least one component ( 3 ) on a printed circuit board ( 2 ) by means of an irreversible color-reversing time-temperature indicator (TTI) ( 6 ), characterized in that after the assembly and soldering of the component ( 3 ) at least one TTI control element ( 6 ) on a given surface at a certain distance from the monitoring component ( 3 ) and as a TTI control element ( 6 ) TTI substances from organic or inorganic salts of transition metals with a molecular decomposition process and homogeneously dispersed in a polymeric matrix with an activation in the relevant temperature range are used, and these TTI substances ( 6 ) have an irreversible visually or machine-verifiable color change in the relevant temperature range and n dependence of the duration of the operation in the relevant temperature range, and thus the temperature load of a component ( 3 ) on a printed circuit board ( 2 ) can be monitored. Method for monitoring the temperature-time loading of components ( 3 ) according to claim 1, characterized in that in addition to the attachment of a TTI control element ( 6 ) a control measuring point ( 5 ), and the distance of both elements ( 5 . 6 ) of the component ( 3 ) is preferably the same. Method for monitoring the temperature-time loading of components ( 3 ) according to claim 1 to 2, characterized in that in addition to the attachment of a TTI control element ( 6 ) and a control measuring point ( 5 ) a checkpoint ( 7 ) and the spacing of the elements ( 5 . 6 . 7 ) of the component ( 3 ) is preferably the same. Method for monitoring the temperature-time loading of components ( 3 ) according to claim 1 to 3, characterized in that the application of the TTI control element ( 6 ) by means of dispenser or pad printing or ink jet or spray nozzle or aerosol jet. Method for monitoring the temperature-time loading of components ( 3 ) according to claim 1 to 4, characterized in that the application of the control point ( 7 ) by means of dispenser or pad printing or ink jet or spray nozzle or aerosol jet. Method for monitoring the temperature-time loading of components ( 3 ) according to claim 1 to 5, characterized in that the application of the control measuring point ( 5 ) by means of screen printing or dispenser or pad printing or ink jet or spray nozzle or aerosol jet. Method for monitoring the temperature-time loading of components ( 3 ) according to claims 1 to 6, characterized in that the TTI control element ( 6 ) is formed in a round or oval or strichbeziehungsweise strip-like shape or represents a temperature value in writing or has a largely free design education. Method for monitoring the temperature-time loading of components ( 3 ) according to claims 1 to 7, characterized in that the TTI control element ( 6 ) on the surface of the printed circuit board ( 1 . 2 ) is arranged on a predetermined surface. Method for monitoring the temperature-time loading of components ( 3 ) according to claims 1 to 8, characterized in that the TTI control element ( 6 ) on the surface of the component ( 3 ) is arranged on a predetermined surface. Method for monitoring the temperature-time loading of components ( 3 ) according to claims 1 to 9, characterized in that several TTI control elements ( 6 ) at different distances to the monitoring component ( 3 ) and the substance of the TTI ( 6 ) is identical. Method for monitoring the temperature-time loading of components ( 3 ) according to claims 1 to 10, characterized in that several TTI control elements ( 6 ), and the temperature range and the time period in which a color change is effective are different. Method for monitoring the temperature-time loading of components ( 3 ) according to claim 1 to 11, characterized in that in addition to the at least one TTI control element ( 6 ) a control element ( 7 ) arranged in the color scheme that the TTI control element ( 6 ), if exceeding the permissible temperature-time load of the component ( 3 ) given is. Method for monitoring the temperature-time loading of components ( 3 ) according to claim 1 to 12, characterized in that a component ( 3 ) such as an LED (light emitting diode) or an IC (integrated circuit) or a passive component is monitored for the integral temperature load over the period of time, in particular an LED ( 3 ). Method for monitoring the temperature-time loading of components ( 3 ) according to claims 1 to 13, characterized in that the color change of the substance of the TTI control element ( 6 ) from largely colorless to whitish in one color or from a color in the direction of translucent or whitish, and optionally the substrate is formed with a contrasting color. Method for monitoring the temperature-time loading of components ( 3 ) according to claim 1 to 14, characterized in that the active temperature-time-indicating substance of the TTI element ( 6 ) of copper (II) hydroxide Cu (OH) 2, nickel (II) chloride hexahydrate NiCl2 · 6H2O, bishexamethylenetetramine cobalt (II) nitrate decahydrate Co (NO3) 2 · 2C6H12N4 · 10H2O or nickel (II) oxalate NiC2O4 homogeneously dispersed in one polymeric matrix. Irreversible Color-Changing Temperature-Time-Indicator (TTI) ( 6 ) for monitoring the temperature-time loading of components ( 3 ) on a printed circuit board ( 2 ) according to the method of claim 1 to 15, wherein at least one TTI control element ( 6 ) on a given surface at a certain distance from the monitoring component ( 3 ) and the TTI control element ( 6 ) TTI substances from organic or inorganic salts of transition metals with a molecular decomposition process and homogeneously dispersed in a polymeric matrix having an activation in the relevant temperature range, and these TTI substances ( 6 ) have an irreversible visually or machine-verifiable color change in the relevant temperature range and in dependence on the duration of the operation in the relevant temperature range, and thus the temperature load of a component ( 3 ) on a printed circuit board ( 2 ) is pictured. Application of an irreversible color change temperature-time indicator (TTI) ( 6 ) for monitoring the temperature-time loading of components ( 3 ) on a printed circuit board ( 2 ) according to the method of claim 1 to 15 and thus for the visual and / or automatic verification of the color change of the TTI control element ( 6 ) and so for monitoring the integral temperature-time load of the component ( 3 ).