WO2007036601A1

WO2007036601A1 - Method, circuit board and test apparatus for testing solder joints

Info

Publication number: WO2007036601A1
Application number: PCT/FI2006/000320
Authority: WO
Inventors: Aulis Tuominen; Ilkka Tuokko
Original assignee: Aulis Tuominen; Ilkka Tuokko
Priority date: 2005-09-30
Filing date: 2006-10-02
Publication date: 2007-04-05
Also published as: EP1949118A1; FI20050982A0

Abstract

The invention relates to a method for testing the reliability of solder joints of electric components (115, 119). Electric components are arranged through solder joints between the first and the second pads arranged in pairs. In a method an electric signal is fed into the electric signal input area (107), and the electric signal is conducted by an electric conductor (105, 130) to the first pad (103), the electric signal is measured at the measurement area (108) which is arranged by electric conductors (106, 125) in series with the second pad (104). According to the invention one or more pad pair groups are formed from the pad pairs, whereby in the method an electric signal is conducted from the electric signal input area (107) simultaneously to two or more first pads (103) of one pad pair group, which two or more first pads are connected in series for conducting electric current. Furthermore, the electric signal is measured at one or more measurement areas (108), each of which is arranged by electric conductors in series with one second pad (104) of one pad pair group. The invention relates further to a circuit board (100) and a test apparatus (500), which has a circuit board according to the invention.

Description

METHOD, CIRCUIT BOARD AND TEST APPARATUS FOR TESTING SOLDER JOINTS

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a method, circuit board and test apparatus for testing solder joints according to the independent claims presented below.

BACKGROUND OF THE INVENTION

Presently the majority of electronic assemblies are manufactured by surface or through hole mounting the components into the circuit boards with solder alloys of tin and lead. There is a long history of using these solder alloys and they have been found quite reliable in respect of their function. There is less experience with lead-free solder alloys, to which manufacturers are required to switch in the near future. As lead-free soldering is becoming more common, there has arisen an ever increasing need for companies to conduct their own solder tests and to compare various materials and process parameters as to their effects on the product.

In presently used test apparatuses solder joints between the components and the circuit boards are tested in such a way that each component is provided with its own pair of measurement channel conductors and the test apparatuses are provided with a data acquisition unit corresponding to the component, which data acquisition unit records the data acquired from the component and its solder joint. The problem with the known test apparatuses is that they require a great number of conductors to the circuit board. For example, every component on the circuit board has its own power supply, so that the number of conductors is double in respect of the number of components to be tested. In addition, the data acquisition units require their own conductors. By using parallel current feeding the number of channels and conductors increases. For these reasons, only a limited number of solder joints of components can be tested with known test apparatuses. Because of their complexity, the known test apparatuses are also quite expensive because of which often only big companies can afford to acquire test apparatuses having so much as 100-200 channels.

If the components are connected in series, the number of conductors required will decrease. The problem is then that, if one component connected in series fails, the components stay without current and the testing is interrupted. In known solutions, components are connected in parallel and each chained component is provided with its own current feeding. Patent publication Fl 104998 B discloses a method, which is based on the fact that a forward diode in the direction of the measurement current is connected over each component being tested and the measurement current is fed from a constant current power source such that the power-off of the current feeding caused by a failed electric component will cause the diode to transfer to a conducting state. The method offers a possibility to automatically continue the testing despite of the failed component, but does not offer a possibility to immediately identify the failed component.

Another patent publication, Fl 104290 B, discloses a method, in which the component identification is possible so that each component connected in the chain is passed by a different number of diodes, whereby each component has its own measurement area. By feeding the components with a constant current and by monitoring their voltages, one can determine from the voltage, if one of the components connected to the diode has failed or if its resistance has changed. The method is relatively simple and functional, but its use for test apparatuses having e.g. hundreds of components is problematic because of its connection arrangement. For example, in a connection arrangement of four integrated circuits thirteen diodes are required for assuring a sufficient voltage margin.

AIMS OF THE INVENTION

The aim of the present invention is to provide a circuit board for testing the reliability of solder joints of the electric components, which circuit board is simple by its construction and inexpensive to manufacture and by means of which circuit board it is possible to test even several hundreds of solder joints of components as a function of time. The aim of the invention is further to provide a test apparatus for testing the reliability of solder joints of electric components, which test apparatus at least partially reduces or eliminates the problems and disadvantages associated with the prior art. The aim of the invention is further a test apparatus for testing the reliability of solder joints of electric components, which test apparatus is simple by its construction and inexpensive to manufacture. Furthermore, the aim of the invention is a test apparatus for testing the reliability of solder joints of electric components, which test apparatus is capable of testing even several hundreds of solder joints as a function of time and which test apparatus makes it possible to identify functioning, failed and/or damaged solder joints immediately.

The aim of the invention is further a method for testing the reliability of solder joints of electric components by means of which method the problems and disadvantages associated with the prior art are at least partially reduced or eliminated. Furthermore, the aim of the invention is further a method for testing the reliability of solder joints of electric components, by which method even several hundreds of solder joints are tested as a function of time and by which method functioning, failed and/or damaged solder joints are additionally immediately identified.

DESCRIPTION OF THE INVENTION

To accomplish i.a. the above-mentioned aims of the invention the invention is characterised by what is presented in the characterising parts of the independent claims presented below. Some preferred embodiments of the invention are described in the dependent claims.

A typical circuit board according to the invention for testing the reliability of solder joints of electric components comprises

- first and second pads for joining an electric component to the circuit board, which first and second pads are arranged in pad pairs so that the first pad of each pad pair can be connected to the second pad of the same pad pair through at least one electric component and its solder joints, - one or more electric signal input areas, which are arranged by electric conductors in series with the first pad, and

- one or more electric signal measurement areas, which are arranged by electric conductors in series with the second pad, It is characteristic for a circuit board according to the invention that one or more pad pair groups are formed from the pads, which pad pair group comprises

- two or more first pads connected in series with each other and

- two or more second pads, whereby one electric signal input area is arranged by electric conductors in series with all the first pads of one pad pair group.

In connection with this application a circuit board refers preferably to a printed circuit board, the material of which is, for example, epoxy laminate (FR-4) or teflon (PTFE). The circuit board can be two-sided, whereby the circuit board can be provided with electric conductors, pads and components on both sides of the circuit board. A circuit board can be laminated in 3, 4, 5, 6, 7, 8, 9 or 10 layers, whereby electrically conducting layers or components are arranged in the circuit board. A circuit board may have metallized and/or unmetallized through holes between the layers, what enables conducting of electricity between the layers. Electric conductors and pads may be e.g. Ni, Au, Ni/Au, Ag, Sn or Pd coated. Electric conductors may be, for example, manufactured of copper. The size and the surface area of pads may vary in accordance with the size of an electric component. The same circuit board may also have pads, which have surface areas of different size.

A typical test apparatus according to the invention for testing the reliability of solder joints of electric components comprises

- at least one circuit board, which comprises

- first and second pads for connecting an electric component to the circuit board, which first and second pads are arranged in pad pairs so that the first pad of each pad pair is connectable to the second pad of the same pad pair through at least one electric component and its solder joints, - one or more electric signal input areas arranged by electric conductors in series with the first pad, and

- one or more electric signal measurement areas arranged by electric conductors in series with the second pad, - at least one signal feeding means connected by electric conductors to the electric signal input area for feeding the electric signal to the pads and

- at least one measuring means connected by electric conductors to the electric signal measurement area for measuring the electric signal coming from the pads. It is characteristic for a test apparatus according to the invention that one or more pad pair groups are formed from the pads of said circuit board, which pad pair group comprises

- two or more first pads connected in series with each other and

In a typical method according to the invention for testing the reliability of solder joints of electric components the electric components are arranged through solder joints between the first and the second pads arranged in pairs, in which method - an electric signal is fed into the electric signal input area,

- the electric signal is conducted by an electric conductor to the first pad,

- the electric signal is measured at the measurement area, which is arranged by electric conductors in series with the second pad.

It is characteristic for a method according to the invention that one or more pad pair groups are formed from the pad pairs, whereby in the method

- an electric signal is conducted from the electric signal input area simultaneously to two or more first pads of one pad pair group, which two or more first pads are conductively connected in series with each other,

- the electric signal is measured at one or more measurement areas, each of which is arranged by electric conductors in series with one second pad of one pad pair group. It has now been surprisingly found that the functioning of solder joints between components and circuit boards can be easily and reliably verified by using a test apparatus, in which the components can be arranged on the circuit board into groups, so that this enables feeding of an electric signal simultaneously to several electric components and measuring of an electric signal in turn from each electric component. This is accomplished by using for the same signal feeding means and measuring means at each electric component for testing, so that when the signal measurement at one electric component has been performed, it is moved over to the next electric component to be tested and its solder joints etc. are tested. According to the invention channelling can be used to verify the functionality of solder joints, so that while the measurement channel is switched on the fed signal can be conducted through the joints of the component to be measured and through the switched-on measurement channel to the measuring means for measuring the signal. Typically, if the channel is switched off, the measurement will not be taken into account. In this case, the measurement data can be collected from the pads and the solder joints arranged in them, for example, as an 8-bit data one measurement channel at a time.

With the aid of the invention the number of conductors required for testing the solder joints can be significantly limited since only one measuring means is required for testing of all of the solder joints on a circuit board. Thus, the price of a test apparatus is low compared to the solutions according to the prior art. A test apparatus according to the invention is furthermore of simple construction and therefore its maintenance is easy.

In a test apparatus according to the invention, the signal feeding means, for example the current/voltage source, is connected by electric conductors, for example, a flat cable, to the electric signal input area and further to at least one first pad, for example through connectors and/or conductors of the circuit board, in which case the first and second pads should be connected to at least one electric component by soldering. An electric signal is fed from the signal feeding means to the signal input area, which signal is further conducted through an electric conductor to a first pad or to two or more first pads. The signal to be fed can be conducted by electric conductors via the solder joint arranged in the first pad and through an electric component and the second solder joint thereon to the second pad and further, for example through electric conductors, to a measurement area. The measurement area can be further connected to the input of the measuring means by using electric conductors. In case of a desired component, the signal passing through the joints of the component is measured by the measuring means, for example by using voltage or current meter. If the solder joints in the pad are conductive, it is assumed that they are in condition and that the electric component is properly connected to the circuit board. If one of the solder joints is not conductive, it can be concluded that the solder joint(s) in question have failed during the testing.

A typical circuit board has pads arranged in groups, so that at least one pad pair group includes several first and second pads. Each circuit board may have two or several pad pair groups, for example 1-10, 8-25, 10-30 or 24. Each group may contain the same number of first and second pads, for example 22 first and 22 second pads, i.e. 22 pad pairs. In this way, at least one electric signal measurement area is arranged by electric conductors in series with at least two second pads, from each of which pad pairs typically one second pad at the most is connected to said series. There are advantageously as many signal measurement areas as there are pad pairs in one pad pair group, and every second pad in each pad pair group is arranged by electric conductors in series with a different electric signal measurement area.

In each group the first pads are arranged in series. In addition, the second pads in each group are arranged in series between different groups, so that at least one second pad of at least one first group is connected in series with one second pad of at least one second group. Thus, it is possible to increase the number of solder joints to be tested on a circuit board without the need to increase the number of inputs of said channelling apparatus. For example, when 528 electric components have been arranged onto the circuit board in 24 groups by soldering, so that there are 22 components in each group, at least one second pad from each group, in this case 24 pads, can be connected in series, in which case 22 inputs are needed for the channelling apparatus.

According to another embodiment of the invention testing of the reliability of solder joints is made possible, so that a diode, e.g. a surface-mount diode, arranged in forward direction with the travelling direction of the signal is connected to the signal feeding means, in which case the diode is arranged between the first and second pad. Thus, when the diode is conducting, the electric signal can pass through the diode from the first pad to the second pad via the solder joints. It is possible to connect, in parallel with the diode, also a resistor, the change of resistance of which value is monitored and the functionality of the solder joints can be concluded from the change of the measurement value.

The test apparatus according to the invention can also be used for testing connections of integrated circuits, whereby said at least one integrated circuit can be arranged between said at least one first pad and at least one second pad according to a so called daisy-chain method, so that the adjacent joints of said at least one integrated circuit can be arranged to be joined together alternatively through the inside of the integrated circuit and alternatively through the bottom of the integrated circuit. According to an embodiment of the invention this is accomplished by connecting in series with integrated circuit a forward conductive diode in the direction of the fed signal.

According to an embodiment of the invention said at least one measuring means comprises at least one channelling apparatus, a so called multiplexer, which has several parallel inputs, the number of which is for example 2, 4, 8, 16, 22 or 24, each input of which can be connected by electric conductors in series with at least one second pad for measuring a signal coming from the pads and from which inputs each can be chosen for electric signal measurement in turn. It can be possible to use channelling apparatuses with even more inputs.

For performing measurements said at least one measuring means can be provided with at least one microcontroller operationally connected to said at least one channelling apparatus, whereby the function of the channelling apparatus can be controlled according to the program code to be programmed to the microcontroller. For example, a separate 16 channels channelling apparatus (multiplexer) can be controlled by 4 bits to select a desired measurement channel. In that case, the desired electric component in turn, solder joints of which are desired to be tested, can be selected programmatically. The arrangement according to this embodiment is accomplished with a separate microcontroller card, in which there are the necessary connectors for connecting to the card of the circuit board according to the invention. The use of the microcontroller enables automation of the testing. In addition, with the microcontroller, the size of the test apparatus can be kept relatively small and its construction simple.

According to an embodiment of the invention all the solder joints on a circuit board are examined in the order determined by a program code programmed in a microcontroller, for example 528 electric components on said at least one circuit board, for example diodes, and their 1056 solder joints. In practice, this is accomplished, so that the anodes of the diodes of one pad pair group on the test board are raised with a weak pull-up to a potential of 5 V. After this, the cathodes of the same diodes are in turn set to 0 V. At that time the potential at the anode is measured. If the potential raised with a weak pull-up has dropped, the diode in question and its joints are considered to be unbroken. The measurement is repeated for each pad pair group. When a joint is detected to be broken for the first time, the measurement is repeated. If the joint is broken, the microcontroller records the time of the failure in its memory.

To facilitate the monitoring and controlling of the testing said test apparatus can be provided with data processing means. According to an embodiment of the invention this has been accomplished, so that said at least one measuring means comprises further at least one computer, which is operationally connected to said at least one microcontroller, for example through RS-232 cable, and a computer program configured to be executed in a memory of the computer, which computer program, while being executed, is configured to control the test apparatus according to the steps of the method according to the invention. If a failed solder joint is detected during the testing, for example an electric component has detached from the circuit board, this failure information and the information on the position of the failed electric component on the circuit board, as well as temperature information, if needed, and/or other information, can be transferred by a microcontroller to the computer for further analysis. Correspondingly, if the solder joint is unbroken, this information and the information on the position of the electric component on the circuit board, and the temperature information, if needed, and/or other information, can be transferred by a microcontroller to the computer for further analysis. When all solder joints have been examined, the measurement can be started again, if necessary. Those electric components and/or solder joints, which have in this way been detected to be failed and/or unbroken, can be easily found on a computer monitor on a graph of the circuit board to be tested. The locations of the components can be identified by coordinates on the graph, whereby the rows are marked, for example, with different numbers and the columns with different letters. Failed components can be marked for example with an "X" and unbroken ones with an "O" or vice-versa. Thus, the tester can immediately see, which joints are possibly unbroken and which are possibly failed. The computer makes it possible to use statistical analysis programs, such as Minitab (Minitab, Inc.) or SAS, for analysing the results, in which case statistical presentations, tables and graphics can be created from collected measurement data.

It is possible to provide a test apparatus according to the invention with at least one measurement sensor, for example, a temperature sensor, in which case the temperature of a solder joint can be monitored by the microcontroller and/or the computer as a function of time as a function of time and a possible failure of the solder joint in a specific temperature can be detected. Accordingly, the measurement sensor can be connected to an analogue converter, which has been arranged in contact with said microcontroller, and which analogue converter converts the analogue measurement data to a digital form for programmatic handling of data. For carrying out the testing by a computer an appropriate interface can be constructed in it. In this interface, for example, the numbers 1-5 can be selected on a computer screen or key pad, whereby choosing of different numbers causes different actions. For example, choosing number 1 starts the testing, choosing number 2 stops the testing, choosing number 3 displays a graphic presentation, choosing number 4 prints the graphic presentation and choosing the number 5 saves the measurement data.

If the test apparatus according to the invention is arranged in operational connection with at least one wireless terminal device, the user can control the test apparatus from remote workstation, for example from a different place than the location of the test apparatus. In that case, test data measured by said measurement means and/or control said the test apparatus can be received with a terminal device, for example a mobile phone or a PDA (Personal Digital Assistant) device. This is accomplished, for example, by providing the test apparatus with a Telnet or Internet connection. The test apparatus can also be provided, for example, with a GSM modem (for example EasyGSM manufactured by Beck IPC GmbH), whereby the test data reading and the controlling of the test apparatus can be made for example with text-messages (Short Message Service, SMS).

The number of components and solder joints to be tested can be significantly increased, if circuit boards according to the invention are connected parallel, such that each circuit board is connected to at least one microcontroller / microcontroller card and/or computer. In an embodiment according to the invention this is accomplished so that the test apparatus according to the invention is connected to a data transfer bus, for example Profibus, whereby the test apparatus can be controlled by at least one computer connected to said bus.

The invention relates further to a method for testing the reliability of solder joints. In a method according to one embodiment of the invention, electric current passing through said at least one electric component is measured for determining the condition of the electric component, in which case a current meter can be arranged in series with the electric component. In a method according to another embodiment of the invention, voltage across said at least one electric component is measured for determining the condition of the electric component, in which case the measurement can be made with a voltmeter.

The invention is further explained by referring to the following drawings, in which,

Figure 1 shows by way of an example a circuit board according to the first embodiment of the invention as seen from the first side,

Figure 2 shows by way of an example a circuit board according to the first embodiment of the invention as seen from the second side,

Figure 3 shows by way of an example a circuit board according to the second embodiment of the invention,

Figure 4 shows by way of an example an arrangement according to the third embodiment of the invention for testing of components, and

Figure 5 shows by way of an example a test apparatus according to the fourth embodiment of the invention.

Figure 1 shows by way of an example a circuit board according to the first embodiment of the invention. The first side 101 of a rectangular double-sided printed circuit board 100 is shown in Figure 1. The circuit board 100 shown in Figure 1 comprises several rectangular first pads 103 and other second pads 104, which are separate from that and the surface areas of which are the same size and the shapes of which are rectangular. In all there are 528 first pads 103 paired with 528 second pads 104 arranged on the test board 100. The pads are arranged further in pairs in 22 columns which are marked in Figure 1 with the letters A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R, S, T, U and V, and in 24 rows which are marked in Figure 1 with consecutive numbers 1 , 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21 , 22, 23 and 24. In Figure 1 the pads of each row form a pad pair group, which has the same number of first and second pads. The first pads 103 in a same row are connected in series with electric conductors 105 on the input side and the second pads in a same column are connected in series with electric conductors 106 on the output side. The areas of the first and second pads increase by rows from row 1 to row 24, such that on first three rows 1 , 2, 3, the areas of the pads 103, 104 are of the same size, on the next three rows 4, 5, 6, slightly larger than previous ones, on the next three rows 7, 8, 9, yet slightly larger, etc. until row 24. The distances between the first and the second pads increase by rows beginning from the first row to row 24, such that the distances between the first and the second pads are the same on the three first rows 1 , 2, 3 and the distances between the first and the second pads on rows 4, 5, 6 are slightly longer than on the previous rows, three following rows 7, 8, 9 have slightly larger distances etc. until row 24.

There are 24 signal input areas 107 separate from each other and 22 signal measurement areas 108 separate from each other arranged in a double row in the edge of the circuit board 100. Each signal input area 107 and each signal measurement area 108 is provided with an internally metallized signal through hole which extends from the first side 101 of the circuit board 100 to the second side 102 of the circuit board 100. There is one signal input area 107 for one row and one signal measurement area 108 for one column, respectively. Thus at least one signal input area 107 is connected with electric conductors 105 of the input side in series with all the first pads 103 on the same row. In addition, at least one signal measurement area 108 is connected with electric conductors 106 of the output side in series with all the second pads 104 in the same column. Furthermore, in Figure 1 , each second pad 104 is connected with electric connectors to at least one internally metallized through hole 109, which is arranged between the first side 101 and the second side of the said circuit board 100. As shown in Figure 1 , 11 signal measurement areas 108 are arranged on the output side with electric conductors 106 to the second pads 104 on the first side 101 of the said circuit board 100. The rest of the 11 signal measurement areas 108 are arranged to the second pads 104 on the second side of the circuit board.

Figure 2 shows by way of an example a circuit board according to the first embodiment of the invention. The second side 102 of the double-sided printed circuit board 100 is shown in Figure 2. The circuit board 100 shown in Figure 2 comprises through holes 109 arranged in relation to the second pads 109, which through holes are arranged in direction of columns of the circuit board 100 and connected in series with each others. The circuit board 100 has a total of 528 through holes, 24 in each column. On the edge of the test board 100 are arranged in a double row 24 separate signal input areas 107 and 22 signal measurement areas 108 corresponding to the number of each columns and rows. 11 signal measurement areas 108 of these are arranged as conducting electricity to second pads on the first side of the circuit board by through holes 109, so that one measurement area 108 is connected to one through hole 109. The rest 11 of the signal measurement areas 108 are arranged to the second pads on the first side 101 of the circuit board.

Figure 3 shows by way of an example a circuit board according to the second embodiment of the invention. The circuit board of this embodiment can be similar to the preceding embodiments. The components to be tested 115, in this case surface-mount diodes, are arranged on the first side of the board in 22 columns and in 24 rows, so that there is a total of 22 x 24 (528) components to be tested and 2 x 22 x 24 (1056) solder joints on the circuit board. There is one surface- mount diode to be tested soldered across each pair of pads so that the anode of the surface-mount diode is soldered to the first pad of the pad pair and the cathode to the second pad of the same pad pair. Same diodes are of the same size on the same row. The size of the surface-mount diodes changes from row 1 to the last row 24, so that on the rows 1-5 the diodes are of size 0603, on the rows 6-12 the diodes are of size 0805 and on the rest of the rows of size 1206.

Figure 4 shows by way of an example a connection arrangement according to the third embodiment of the invention. In this embodiment both an integrated circuit 115 and a diode 119 connected in series with it are arranged by soldering between the first pad 103 and the second pad 104 of the printed circuit board. The integrated circuit 115 is arranged to the circuit board with a daisy-chain method, so that the joints of the circuit are alternately brought to the substrate side and to the circuit side. In Figure 4 the connection brought from the circuit side is shown in a dashed line 117 and a connection made to the substrate with a solid line 118. In addition to this, other different integrated circuits connected with a daisy-chain method can be used.

Figure 5 shows by way of an example a test apparatus according to the fourth embodiment of the invention. The test apparatus 500 comprises of three components: measuring means 128, for example a microcontroller card, signal feeding means 129, for example a power supply, and a circuit board 100. The circuit board 100 is a double-sided epoxy laminate sheet, FR4, the dimensions of which can be 1.6 x 162 x 220 mm³. The measuring means 128 are connected to the circuit board 100 with a flat cable 125. The measuring means 128 are also connected with an RS-232 cable 126 to a computer 127, which has been provided with user interface. The signal feeding means 129 is connected to the circuit board 100 with a flat cable 130. The test apparatus 500 shown in Figure 5 can also be controlled by a portable terminal 124, e.g. a phone. This is made possible for example by connecting a GSM modem connection to the apparatus.

Testing with a test apparatus 500 is performed such that anodes of the diodes of one row on the circuit board 100 are raised to a potential of 5 V with weak pull-up. After this the cathodes of the same diodes are set to 0 V group by group. At the same time the voltage of the anodes is measured. If the pulled-up anode potential has dropped, the diode in question and its connections are considered to be flawless. This measurement is repeated for each pad pair group. When a connection is detected to have failed for the first time the measurement is repeated. If the connection is broken, the test apparatus 500 records the time of the failure in its memory. The failure times can be downloaded to the computer 127 at any time through the serial port.

It is obvious for a person skilled in the art that the invention is not restricted to the embodiments presented above, but the invention may be modified within the scope of protection of the claims. For example conductive or non-conductive adhesives, wire-bonding, e.g. with chip-on-board components, or crimp connections can be used instead of solder joints. Mechanical components can be used instead of electric components. The inventive idea can also be used in security surveillance of buildings, the controlling of components like transistors and triacs, monitoring production machines in factories or in the testing of cables, for example bending testing of cables.

Claims

1. A method for testing the reliability of solder joints of electric components (115, 119), which electric components are arranged through solder joints between the first and the second pads arranged in pairs, in which method

- an electric signal is fed into the electric signal input area (107),

- the electric signal is conducted by an electric conductor (105, 130) to the first pad (103),

- the electric signal is measured at the measurement area (108) which is arranged by electric conductors (106, 125) in series with the second pad

(104), characterized in that one or more pad pair groups are formed from the pad pairs whereby in the method

- an electric signal is conducted from the electric signal input area (107) simultaneously to two or more first pads (103) of one pad pair group which two or more first pads (103) are conductively connected in series with each other,

- the electric signal is measured at one or more measurement areas (108), each of which is arranged by electric conductors in series with one second pad (104) of one pad pair group.

2. A method according to claim 1 , characterized in that there are two or more pad pair groups and that one electric signal measurement area (108) is arranged by electric conductors in series with at least two second pads (104), from which each pad pair group to said series is connected at most one second pad (104), whereby in the method

- the electric signal is conducted in turn to two or more first pads (103) of each pad pair group.

3. A method according to claim 1 , characterized in that in the method the electric signal is measured in turn at each measurement area (108) by channelling the measurement to said measurement area (108).

4. A method according to claim 1 , characterized in that in the method electric current passing through at least one electric component (115, 119) is measured for determining the condition of the electric component (115, 119).

5. A method according to claim 1 , characterized in that in the method the electric signal is fed to said at least one electric component (115) through a forward conductive diode (119) connected in series with it.

6. A method according to claim 1 , characterized in that in the method measured data is collected and processed by at least one computer (127) utilizing a computer program executed in the computer's (127) memory.

7. A method according to claim 6, characterized in that in the method collected and processed data is sent to a wireless terminal (124).

8. A circuit board (100) for testing the reliability of solder joints of electric components (115, 119), which circuit board (100) comprises

- first and second pads for connecting the electric component (115, 119) to the circuit board (100), which first and second pads (103, 104) are arranged in pad pairs so that the first pad (103) of each pad pair can be connected to the second pad (104) of the same pad pair through at least one electric component (115, 119) and its solder joints,

- one or more electric signal input areas (107) which are arranged by electric conductors (105) in series with the first pad (103), and

- one or more electric signal measurement areas (104) which are arranged by electric conductors (106) in series with the second pad (104), characterized in that one or more pad pair groups are formed from the pads (103, 104), which pad pair group comprises - two or more first pads (103) connected in series with each other and

- two or more second pads (104), whereby one electric signal input area is arranged by electric conductors (105) in series with all the first pads (103) of one pad pair group.

9. A circuit board according to claim 8, characterized in that there are two or more pad pair groups and that one electric signal measurement area (108) is arranged by electric conductors (106, 125) in series with at least two second pads (104) from which each pad pair group at most one second pad (104) is connected to said series.

10. A circuit board according to claim 9, characterized in that each pad pair group has an equal number of pad pairs.

11. A circuit board according to claim 10, characterized in that the number of electric signal measurement areas (108) equals the number of pad pairs in one pad pair group, and that every second pad (104) of each pad pair group is arranged by electric conductors in series with a different electric signal measurement area.

12. A test apparatus (500) for testing the reliability of solder joints of electric components (115, 119), which test apparatus (1 ) comprises - at least one circuit board (100), which comprises

- first and second pads (103, 104) for connecting an electric component (115, 119) to the circuit board (100), which first and second pads are arranged in pad pairs so that the first pad (103) of each pad pair is connectable to the second pad (104) of the same pad pair through at least one electric component (115) and its solder joints,

- one or more electric signal input areas (107) arranged by electric conductors (105) in series with the first pad (103), and

- one or more electric signal measurement areas (108) arranged by electric conductors (106) in series with the second pad (104), - at least one signal feeding means (129) connected by electric conductors

(130) to the electric signal input area (107) for feeding the electric signal to the pads (103, 104) and

- at least one measuring means (128) connected by electric conductors (125) to the electric signal measurement area (108) for measuring the electric signal coming from the pads (103, 104), characterized in that the circuit board (100) is according to claim 8.

13. A test apparatus (500) according to claim 12, characterized in that said at least one measuring means (128) comprises at least one channelling apparatus, a so called multiplexer, which has several parallel inputs each of which can be connected by electric conductors (125) in series with at least one electric signal measurement area (108) for measuring electric signals coming from the pads.

14. A test apparatus (500) according to claim 13, characterized in that said at least one measuring means (128) comprises further at least one microcontroller operationally connected to said channelling apparatus for controlling said channelling apparatus.

15. A test apparatus (500) according to claim 14, characterized in that said at least one measuring means (128) comprises further a computer (127) which is operationally connected to said at least one microcontroller and a computer program configured to be executed in a memory of the computer, which computer program while being executed is configured to control the test apparatus (500) so that the apparatus executes the steps of a method according to claim 1.

16. A test apparatus (500) according to claim 12, characterized in that the test apparatus (500) can be arranged to be in operational connection with at least one wireless terminal (124) for receiving the data measured by using the said measuring means (128) and controlling the said test apparatus (500) by using the said terminal (124).

17. A test apparatus (500) according to claim 12, characterized in that said at least one electric component is a diode (119).

18. A test apparatus (500) according to claim 13, characterized in that said at least one electric component is an integrated circuit (115).

19. A test apparatus (500) according to claim 18, characterized in that said at least one integrated circuit (115) can be arranged between said at least one first pad (103) and at least one second pad (104) according to a so called daisy-chain configuration so that the adjacent joints of said at least one integrated circuit (115) can be arranged to be joined together alternatively through the inside of the circuit and alternatively through the bottom of the integrated circuit.