JP2734065B2 - Pass / fail judgment method of preliminary test in reflow - Google Patents

Description

Description: BACKGROUND OF THE INVENTION The present invention relates to a pass / fail judgment method of a preliminary test in reflow, and relates to a display unit such as a recording paper for displaying a measurement result of a temperature change of a substrate conveyed in a heating chamber. By displaying a pass / fail judgment curve having an allowable width together with the measurement results, the pass / fail judgment can be easily performed.

(Prior Art) A board on which electronic components such as an IC chip, an LSI chip, a resistor chip, and a capacitor chip are mounted by the paste solder is sent to a reflow device, and the paste solder is heated. This heat treatment has processing conditions such as temperature conditions and temperature gradients. For example, if the temperature is too high, IC or LSI
Etc. are thermally destroyed, and if the temperature is too low, the solder will not be sufficiently cured. Such processing conditions vary depending on the type of the board, electronic components, solder, etc., or the mounting density of the electronic components. Therefore, when the type of the mounting substrate is changed, the processing conditions must also be changed. .

For this reason, a preliminary test is generally performed before a full-scale heating process is performed by the reflow device. Conventionally, this preliminary test is performed by blowing hot air or cold air onto the substrate, the temperature of the heater of the reflow device, the speed of the substrate transport conveyor, and the substrate. In addition to appropriately setting the rotation speed of the fan to be attached, a temperature sensor is mounted on the sample substrate, the sample substrate is transported in a heating chamber, and the result is recorded on a recording paper to determine whether the result is acceptable. Had become.

FIG. 5 shows the temperature curve recorded on the recording paper as described above. The pass / fail judgment is made by applying a scale to this graph and determining whether the preheating section, the soaking section, the reflow section, and the cooling section. Temperature or time, or a temperature gradient such as a rising gradient of a preheating portion or a falling gradient of a cooling portion.

(Problems to be Solved by the Invention) However, the above-mentioned conventional means determines pass / fail by measuring the temperature curve by applying a scale to the recording paper. It took a lot of trouble and time.

In particular, if the result of the above pass / fail judgment is "No", the temperature of the heater, the speed of the conveyor and the fan, etc. must be readjusted and the test using the sample substrate must be performed again. Since it has to be repeated until a judgment is obtained, an extremely large amount of time and labor is required.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a method capable of easily determining whether or not a reflow preliminary test is successful.

(Means for Solving the Problems) For this purpose, the present invention provides a method in which a temperature sensor is mounted on a board on which electronic components are mounted by paste-like solder, and the board is transported through a heating chamber of a reflow apparatus. When the temperature change of the substrate is measured and the measurement result is displayed on the display unit of the recording display device, a band-shaped pass / fail judgment curve having an allowable width is displayed on the upper display unit together with the temperature change curve of the substrate by the above measurement. And the pass / fail judgment curve has a preheating section, a soaking section, a reflow section, and a cooling section, and the allowable width of these four sections is determined according to the strictness of required conditions. The allowable width of the reflow section is narrower than the allowable width of the preheating section and the soaking section.

(Operation) In the above configuration, the pass / fail judgment is made by checking the degree of deviation of the measured temperature curve from the pass / fail judgment curve. In this case, the quality of the temperature curve is determined for each of the preheating section, the soaking section, and the reflow section. However, since the quality of the reflow depends particularly on the appropriateness of the temperature control of the reflow section, the allowable width of the reflow section is reduced. Strictly make a pass / fail decision.

Example Next, an example of the present invention will be described with reference to the drawings.

FIG. 1 is a side view of the reflow apparatus, wherein 1 is a heating chamber, and 2 is a conveyor for transporting the substrate 3 in the heating chamber 1. In the heating chamber 1, a heater H1 such as a heat block is provided.
To H9 are disposed above and below the substrate 3 on the conveyor 2. Above the substrate 3, fans F1 to F3 for blowing hot air onto the substrate 3 and the substrate 3 near the outlet of the heating chamber 1 are provided.
A cooling fan F4 that blows cold air is provided.

FIG. 2 shows a sample substrate 3 to be subjected to a preliminary test, on which an electronic component P is mounted by a paste solder 4. Reference numerals 5 (5a to 5c) denote thermocouples as temperature-sensitive sensors mounted on the upper surface of the substrate 3, which are mounted on the central portion and both side portions of the substrate 3 with an adhesive tape 6. In the present embodiment, three temperature sensors 5a to 5c are used to measure the temperature changes at three points on the substrate 3. However, the number of temperature sensors is arbitrary. By measuring the temperature changes at a number of points, a fine pass / fail decision can be made.

As shown in FIG. 1, the temperature sensors 5a to 5c
It is connected to a computer 12 via a converter 11, and a printer 13 as a display device is connected to the computer 12, and a recording paper 14 as a display unit is attached to a temperature sensor 5a.
The temperature change curve measured by ~ 5c is recorded. Note that the display device may be an image device such as a CRT.

FIG. 3 is a control block diagram showing each of the fans F1 to F3.
Controllers A1 to F4 and motors M1 to M5 for driving conveyor 2
A5 and the control units B1 to B9 of the heaters H1 to H9 are connected to a computer.
The devices F1 to F4, 2, and H1 to H9 are selectively connected to the centralized control by the computer 12 or can be independently controlled.

FIG. 4 is a graph showing a temperature curve of the recording paper 14 obtained by transporting the substrate 3 in the heating chamber 1, wherein a, b, and c indicate the respective sensors 5a, 5b, and 5c. It is a temperature curve. N is a band-shaped pass / fail judgment curve, and the operator judges pass / fail based on the degree of deviation between the temperature curves a to c and the curve N. The curve N includes a preheating section, a soaking section, a reflow section (solder melting section), and a cooling section, and the widths D1, D2, and D3 of the curve N mean allowable widths of the respective sections. Incidentally, the curve N is set based on the following factors, for example.

(1) Rising slope of preheating section (2.2 ° C / sec up to 150 ° C) (2) Temperature and time of soaking section (150 ° C to 170 ° C continued for 60 to 75 seconds) (3) Temperature of reflow section and its Time, especially the highest temperature (20
(0 ° C or more and 20 seconds or less, 220 ° C or more and 10 seconds or less, maximum 225 ° C) (4) Falling slope of cooling part (2-3 ° C / sec down to 140 ° C) Of course, these factors are for board, solder, and electronic components Depends on the type of Among the factors (1) to (4), the factor (3) relating to the reflow section is particularly important. Therefore, as is clear from the figure, the allowable width D3 of the reflow is narrow, and the pass / fail judgment is strictly performed. Also, considerable temperature variation is allowed, and the widths D2 and D3 of the preheating section and the soaking section are set to be considerably large.
The allowable width D of the curve N is set according to the strictness of the required conditions.

If the test result is determined to be “OK”, then a full-fledged reflow is performed. If it is determined as “No”,
The temperatures of the heaters H1 to H9 and the speeds of the conveyor 2 and the fans F1 to F5 are readjusted, and the above test is performed again. This test is repeatedly performed until a "Pass" judgment is obtained.
The criteria for the pass / fail is arbitrary. For example, in the reflow section, it is desirable to determine “No” even if the curve N is slightly deviated from the curve N. "". The preliminary test is performed prior to full-scale reflow, but during full-scale reflow,
In order to check whether reflow is performed normally, a sample substrate may be appropriately extracted and performed.

The test data is stored as a database of the computer 12, and data relating to various types of substrates is stored over a long period of time. Therefore, when a new board appears, by extracting the data closest to the board from the database, and controlling the devices M1 to M5, 2, H1 to H9 based on the data,
As a result, the result of "go" is obtained with a higher probability, so that unnecessary repetition of the preliminary test by trial and error can be eliminated.

(Effects of the Invention) According to the present invention, it is possible to determine whether pass / fail of the reflow preliminary test is extremely simple and accurate. Although the quality of the temperature curve is determined for each of the preheating section, the soaking section, and the reflow section, the quality of the reflow depends on the appropriateness of the temperature control of the reflow section in particular. By strictly performing the pass / fail determination, a highly reliable pass / fail determination can be performed.

[Brief description of the drawings]

1 shows an embodiment of the present invention. FIG. 1 is a side view of a reflow device, FIG. 2 is a perspective view of a substrate, FIG. 3 is a block diagram, FIG. 4 is a temperature curve diagram, and FIG. The figure is a temperature curve diagram of the conventional means. DESCRIPTION OF SYMBOLS 1 ... Heating chamber 3 ... Substrate 4 ... Paste solder 13 ... Record display device 14 ... Record display part P ... Electronic components 5a-5c ... Temperature sensor

Claims (1)

(57) [Claims] A temperature sensor is mounted on a board on which electronic components are mounted by solder paste, and a temperature change of the board is measured while transporting the board in a heating chamber of a reflow device. In displaying on the display unit of the recording display device, the upper display unit, along with the temperature change curve of the substrate by the above measurement, to display a band-shaped pass / fail determination curve having an allowable width, and the pass / fail determination curve, It has a preheating part, a soaking part, a reflow part, and a cooling part, and the allowable width of these four parts is set according to the strictness of the required conditions. A pass / fail judgment method for a preliminary test in reflow, characterized in that the allowable width is narrower than the allowable widths of the preheating section and the soaking section.