WO2020248555A1 - Pcb dynamic conduction reliability test method - Google Patents

Abstract

A PCB dynamic conduction reliability test method, which is implemented by adopting the following steps: S1, preparing for measurement; S2, performing heating test; S3, performing cooling test; S4, establishing a correspondence between temperature and resistivity; and S5, performing measurement data analysis.

Description

A Kind of PCB Dynamic Conduction Reliability Test Method Technical field

The invention relates to the technical field of PCB testing, in particular to a PCB dynamic conduction reliability testing method.

Background technique

Printed Circuit Board (PCB" for short), also known as printed circuit board or printed circuit board. Its main function is to connect various electronic components and components through circuits to play the role of conduction and transmission. It is a key electronic interconnection of electronic products.

Almost every kind of electronic equipment is inseparable from the printed circuit board, because it provides mechanical support for the fixed assembly of various electronic components, realizes the wiring and electrical connection or electrical insulation between them, and provides the required electrical characteristics. Its manufacturing quality It directly affects the stability and service life of electronic products, and affects the overall competitiveness of system products. It is known as the "mother of electronic products".

The PCB production process is very complicated. The birth of a PCB requires drilling, copper sinking, electroplating, etching... and many other processes. In each process, it may be due to equipment parameter problems, external environmental problems, or personnel operation problems. , Or due to process formulation issues, these many possible factors are mixed together, which may cause hidden quality problems in PCB products.

In the production process of electronic products, various electronic components need to be mounted and soldered on the PCB board, so the PCB needs to undergo high-temperature production processes such as hot-air reflow oven or wave soldering.

In such high-temperature manufacturing processes, the thermal expansion of the PCB board may cause problems in the connection of the inner circuit. Such problems will affect the integrity of the signal transmission of the PCB circuit, and there may also be a potential risk of failure of electronic products.

Usually this kind of problem is higher in PCB board risk and has a wide range of influence, which will cause huge economic compensation losses for PCB board production factories.

At present, PCB board simulation test tests mostly use tests such as IR test, hot oil test, thermal shock, etc. The above test methods are to compare the on-resistance at the same temperature before and after heating or cooling, and return to the same temperature. The cracks between the back conducting lines may also be restored to the connected state. This method cannot find out the specific temperature at which the cracks are generated, and even the cracks actually produced cannot be found.

Therefore, it is necessary to set up a PCB dynamic conduction reliability test, which can make up for the shortcomings of the above test methods, and can find out the temperature range caused by the specific cracks.

Summary of the invention

The purpose of the present invention is to solve the shortcomings in the prior art, and proposes a PCB dynamic conduction reliability test method.

In order to achieve the above objective, the present invention adopts the following technical solution, a PCB dynamic conduction reliability test method, which is characterized in that it specifically includes the following steps.

S1. Preparation for measurement: Connect the four-wire micro-resistance meter with heat-resistant wires at both ends of the test circuit, put the test board in the oven, and measure the resistance of both ends of the test circuit. The subsequent heating and measurement process is incorrect Do any movement of the oven, test board, tester and connecting wire.

S2. Heating test: The oven is heated, and the maximum temperature generally does not exceed the maximum temperature that the PCB can withstand. During the heating process, the temperature of the oven and the resistance value displayed by the corresponding four-wire resistance meter are dynamically recorded.

S3. Cooling test: Turn off the heating of the oven to cool down, and dynamically record the temperature of the oven and the corresponding resistance.

S4. Establish the corresponding relationship between temperature and resistivity. Temperature and resistivity have a linear relationship. PCB wire is copper, and the resistivity of copper at different temperatures can get the basic corresponding relationship by looking up the table, or through actual measurement For a uniform wire with a known length and cross-sectional area, the corresponding relationship between temperature and resistivity is as follows:

Resistivity=0.0165+temperature℃*6.8*10 ^-5 Resistivity unit: ohm*square millimeter/meter

The resistivity of different copper content is different, and the resistivity of different conductor materials is also different. The above corresponding relationship will vary according to the copper content and conductor material.

S5, measurement data analysis

Resistance = resistivity * wire length / wire cross-sectional area Unit: Ω

Resistance/resistivity = wire length/wire cross-sectional area Unit: meter/square millimeter

When stress is generated under the temperature change, the length of the wire remains unchanged, and the cross-sectional area of the wire decreases sharply (crack appears), the value of the length/cross-sectional area will increase sharply, which is reflected in: the measured resistance/standard resistivity The temperature and resistance values actually measured are set up as follows:

Temperature ℃	Measured resistance	The resistivity of copper at different temperatures	Length/cross-sectional area
20	R 20	0_01786	R 20 /0_01786
25	R 25	0_0182	R 25 /0_0182
30	R 30	0_01854	R 30 /0_01854
35	R 35	0_01888	R 35 /0_01888
40	R 40	0_01922	R 40 /0_01922
-	-	-	-
150	R 150	0_0267	R 150 /0_0267
-	-	-	-
260	R 260	0_03418	R 260 /0_03418
-	-	-	-

In the above table, when the value of length/cross-sectional area exceeds the average value by 10%, it is considered that a crack has occurred at this time, and the corresponding temperature value is found to know what temperature range caused the crack.

At different temperatures, the expansion rate of the material is different, and different forces are generated. Under the action of multiple combined forces, the weak part of the bonding force will be torn or completely separated. At this time, it shows a significant degree of PCB trust. Defects, such as separation of hole bottom, thinning hole breakage, interface hole breakage, through hole ICD, blind hole ICD, etc.

Compared with the prior art, the present invention provides a method for testing the reliability of PCB dynamic conduction. Compared with the prior art, the present invention can separate PCB products such as: hole bottom separation, blind hole broken hole, and through hole through 5 steps of testing. Broken holes, radium shot penetration, residual glue at the bottom of the hole, foreign body broken holes, through-hole ICD, blind hole folding plating, through hole folding plating, plating hole broken and other problems are detected.

In the process of testing, the present invention will not cause damage to good PCB products, and products that pass the test will not affect product shipments, which is a non-destructive test;

The test of the present invention consumes relatively short time, has good timeliness, and can quickly feedback the defect problem, so that the production process can be adjusted and improved in time, and unnecessary scrap loss can be avoided.

Detailed ways

In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with specific embodiments.

It should be understood that the specific embodiments described here are only used to explain the present invention, but not to limit the present invention.

Example 1

A PCB dynamic conduction reliability test method, which specifically includes the following steps:

S1. Preparation for measurement: select a test circuit with vias, connect the four-wire resistance tester with heat-resistant wires (heat-resistant 300℃) at both ends, weld DRIVE+ and DRIVE- at the outermost end, and weld SENSOR+ close to the outermost end SENSOR-, DRIVE+ and SENSOR+ are at the same end, DRIVE- and SENSOR- are at the other end, the measuring range of the resistance meter is set to 20mΩ, the measurement speed is slow test, and the test board is placed in the oven with the highest temperature resistance of 200℃ , Carry out resistance measurement on both ends of the test loop, and do not move the oven, test board, tester and connecting wire in the subsequent heating, cooling and measurement process.

S2, heating test: when the measured value change range is less than 5% at normal temperature, the oven is heated up, the highest temperature is set to 155℃, and the heating rate is lower than 10℃/min, so that the temperature of the test board and the oven display The temperature error does not exceed 5℃. Record the temperature of the oven and the corresponding resistance every 5-10℃.

S3. Cooling test: No cooling test is done.

S4. There is a linear relationship between temperature and resistivity. The wire of the PCB is copper, and the resistivity of copper at different temperatures can be obtained by looking up the table. The basic corresponding relationship is as follows:

Resistivity=0.0165+temperature℃*6.8*10 ^-5 Resistivity unit: ohm*square millimeter/meter

Resistance = resistivity * wire length / wire cross-sectional area

S5, measurement data analysis

Resistance/resistivity=length/cross-sectional area

When stress is generated under the temperature change, the length of the wire remains unchanged, and the cross-sectional area of the wire decreases sharply (crack appears), the value of the length/cross-sectional area will increase sharply, which is reflected in: the measured resistance/standard resistivity The temperature and resistance values actually measured are set up as follows:

In the above table, the fluctuation range of the length/cross-sectional area compared with the average value is less than 5%. Generally, when the value of the length/cross-sectional area exceeds the average value by 10%, it is considered that a crack has occurred at this time, so it can be considered as the circuit of this measurement. The conduction reliability is good, and there is no crack in the range of 33-155°C.

The above are only preferred specific embodiments of the present invention, but the protection scope of the present invention is not limited to this. Anyone familiar with the technical field within the technical scope disclosed by the present invention, according to the technical solution of the present invention The equivalent replacement or change of the inventive concept thereof shall be covered by the protection scope of the present invention.

Claims (6)

1. A PCB dynamic conduction reliability test method, implemented by the following steps:

   S1, prepare for measurement;

   S2, heating test;

   S3, cooling test;

   S4. Establish the corresponding relationship between temperature and resistivity;

   S5. Analysis of measurement data.
2. The test method according to claim 1, wherein step S1 is: connect the two ends of the test circuit to a four-wire resistance meter with heat-resistant wires, put the test board in the oven, and measure the resistance of both ends of the test circuit , The oven, test board, tester and connecting wire are not moved in the subsequent heating and measurement process.
3. The test method according to claim 1, wherein step S2 is: heating the oven, the highest temperature generally does not exceed the highest temperature that the PCB can withstand, and dynamically record the oven temperature and the corresponding four-wire resistance meter display during the heating process Resistance.
4. The test method according to claim 1, wherein step S3 is: turning off the heating of the oven to cool down, and dynamically recording the temperature of the oven and the corresponding resistance value.
5. The test method according to claim 1, wherein step S4 is: establishing the corresponding relationship between temperature and resistivity, the temperature and resistivity are in a linear relationship, the wire of the PCB is copper, and the resistivity of copper at different temperatures passes the look-up table The basic corresponding relationship can be obtained, or through actual measurement of a uniform wire with a known length and cross-sectional area, the corresponding relationship between temperature and resistivity is as follows:

   Resistivity=0.0165+temperature℃*6.8*10 ^-5 Resistivity unit: ohm*square millimeter/meter

   The resistivity of different copper content is different, and the resistivity of different conductor materials is also different. The above corresponding relationship will vary according to the copper content and conductor material.
6. The test method according to claim 1, wherein step S5 is: analyzing the measurement data:

   Resistance = resistivity * wire length / wire cross-sectional area Unit: ohm

   Resistance/resistivity = wire length/wire cross-sectional area Unit: m/square millimeter

   When stress is generated under the temperature change, the length of the wire remains unchanged, and the cross-sectional area of the wire decreases sharply (crack appears), the value of the length/cross-sectional area will increase sharply, which is reflected in: the measured resistance/standard resistivity When the value of length/cross-sectional area exceeds the average value by 10%, it is considered that a crack has occurred at this time. Find the corresponding temperature value and you can know what temperature it is. The interval created a gap.