JP2006093171A - Heat screening method of electronic component - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a heat screening method which prevents a decline in solder wettability after heat screening in an electronic component which uses a lead frame as a terminal electrode. <P>SOLUTION: Heat screening is conducted on the electronic component in an nitrogen reflow furnace under the conditions that, after a heat treatment is conducted in a nitrogen atmosphere at an oxygen density of 500 ppm or below until the surface temperature of the electronic component becomes 210-280°C, a cooling process is conducted in a nitrogen atmosphere at an oxygen density of 500 ppm or below. By this method, the solder wettability is kept at the same level as before the heat treatment. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an electronic component inspection method, and more particularly to a thermal screening method that improves solder wettability of an electronic component using a lead frame as a terminal electrode.

Conventionally, in an electronic component having a lead frame, an inspection method by thermal screening is used for the purpose of removing defective products whose electrical characteristics deteriorate due to thermal stress during soldering. In the thermal screening method, the heat treatment after the formation of the exterior resin is performed in a fluorine-based inert liquid or its vapor phase, and the cooling after the heating is performed in the air (for example, see Patent Document 1).
Japanese Patent Laid-Open No. 06-036976 (No. 4-Fig. 3)

  However, there was a problem that the surface of the lead frame was oxidized and discolored (deformed) during cooling, and the solder wettability was lowered, so that it was required to keep the solder wettability equivalent to that before the thermal screening. .

  Furthermore, since the fluorine-based inert liquid is volatilized out of the apparatus when the electronic component is put into the heater or taken out of the heater, the liquid needs to be replenished. There is a problem that the manufacturing cost of parts increases, and a thermal screening method with a low running cost is required.

  The present invention solves the above-described problems, and an object of the present invention is to provide a thermal screening method capable of maintaining the solder wettability after heat treatment of an electronic component with a lead frame equivalent to that before heat treatment.

  That is, the present invention includes a heat treatment step of heating an electronic component having a lead frame as a terminal electrode in a nitrogen atmosphere, and a cooling treatment step of cooling the electronic component in a nitrogen atmosphere. It is.

  Further, the present invention is the electronic part thermal screening method characterized in that the oxygen concentration in the heat treatment step and the cooling treatment step is 500 ppm or less.

  Furthermore, the electronic component thermal screening method is characterized in that the surface temperature of the electronic component during the heat treatment is 210 to 280 ° C.

  In the present invention, heat treatment for electronic screening using a lead frame as a terminal electrode and subsequent cooling are performed in a nitrogen atmosphere without introducing a product whose electrical characteristics deteriorate due to thermal stress during soldering. By preventing oxidation of the lead frame surface, the solder wettability can be kept equal to that before the thermal screening.

  In addition, since an expensive fluorine-based inert liquid is not used, the manufacturing cost required for thermal screening of electronic components can be reduced.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a side view of a nitrogen reflow furnace used in the present invention, in which a loader 11 is provided at the inlet and an unloader 12 is provided at the outlet to automatically feed / wind up the lead frame.
FIG. 2 is a cross-sectional view of the portion of the nitrogen reflow furnace indicated by the dotted line in FIG. Four heating units 2a, 2b, 2c, and 2d and one cooling unit 3 are provided, and nitrogen is supplied from the pipe 1. Furthermore, the oxygen concentration in the nitrogen reflow furnace is adjusted by adjusting the flow rate of nitrogen.

  Further, a convection fan 5 is provided in the furnace in order to reduce temperature variation in the furnace of the nitrogen reflow furnace.

[Example 1]
The temperature was set so that the temperature of the electronic component surface was 260 ° C. using the nitrogen reflow furnace of FIG. Furthermore, the oxygen concentration in the nitrogen reflow furnace was set to 100 ppm.

[Examples 2 to 5]
The conditions were the same as in Example 1 except that the oxygen concentrations in the nitrogen reflow furnace were 500 ppm, 0.1%, 1%, and 10%, respectively.

(Conventional example)
The heat treatment was performed by a vapor phase method (heating in the vapor phase of a fluorine-based inert liquid) so that the temperature of the electronic component surface was 240 ° C.

  The electronic parts according to Examples 1 to 5 and the conventional example were screened by a nitrogen reflow furnace, and the surface of the lead frame after the processing was observed. The results are shown in Table 1.

  In addition to the temperature of the electronic component surface according to Example 1, the leakage current value after screening 1,000 electronic components under six conditions of 200, 210, 230, 280, and 290 ° C. was exceeded and exceeded the standard value. Confirmed the number of products. The screening process and leakage current measurement were performed up to three times. The results are shown in Table 2.

  From Table 1, in Examples 1 and 2, there was no discoloration of the frame due to oxidation after the thermal screening treatment. However, in Examples 3 to 5 in which the oxygen concentration was 0.1% or more and the conventional example of the vapor phase treatment, discoloration (degeneration) of the frame occurred.

From Table 2, when the maximum temperature of the surface of the tantalum solid electrolytic capacitor was 200 ° C., the thermal screening could not be completed by one heat treatment, and the second time was out of specification. Under this temperature condition, since the screening process cannot be performed once, it is necessary to carry out it twice or more.
In addition, at 210 to 280 ° C., non-standard occurred after one time, but there was no non-standard value at the second and third times, so the effect of thermal screening was obtained by one heat treatment.
Furthermore, at 290 ° C., a non-standard occurred after one reflow, and the number of products out of the standard increased at the second and third times. This indicates that since the temperature is high, the product is deteriorated by the heat treatment.
From the above, it is desirable that the thermal screening is performed once when the temperature of the surface of the electronic component is in the range of 210 to 280 ° C.

Furthermore, the solder wettability after the thermal screening process was confirmed. As a pretreatment before measurement of solder wettability, 121 ° C. and 100% unsaturated PCT were performed for 8 hours. The solder wettability was measured by a rapid heating temperature raising method, using 96.5% tin, 3.0% silver and 0.5% copper as the solder, and the temperature of the solder bath at 245 ° C. The measurement was performed three by each. FIGS. 3 and 4 show the zero cross time (the time when the solder begins to get wet, the better the wettability, the better) and the wet-up time of Examples 1 to 5 and the conventional example, respectively. 3 and 4, Examples 1 and 2 were within 2 seconds shorter than the conventional example, and an improvement effect was obtained.
However, in Example 3 in which the oxygen concentration is 0.1%, the zero cross time and the wetting time are the same as in the conventional example, but discoloration is observed in the lead frame, and Example 4 in which the oxygen concentration is 1% or more. In No. 5, since the zero crossing time and the wetting time increase, the oxygen concentration in the nitrogen reflow furnace is desirably 500 ppm or less.

It is a side view of the nitrogen reflow furnace by the Example of this invention. It is sectional drawing of the nitrogen reflow furnace by the Example of this invention. It is the figure which showed the zero crossing time of the solder wettability of Examples 1-5 of this invention and a prior art example. It is the figure which showed the finishing time of the solder wettability of Examples 1-5 of this invention and a prior art example.

Explanation of symbols

1 Nitrogen piping 2a Heating part 1
2b Heating part 2
2c Heating part 3
2d heating unit 4
3 Cooling unit 4 Heater 5 Fan 6 Oxygen meter 7 Conveyor 8 Nitrogen flow meter 9 Nitrogen reflow furnace 10 Lead frame 11 Loader 12 Unloader

Claims (3)

  An electronic component thermal screening method comprising: a heat treatment step of heating an electronic component having a lead frame as a terminal electrode in a nitrogen atmosphere; and a cooling treatment step of cooling the electronic component in a nitrogen atmosphere.   The thermal screening method for electronic parts, wherein the oxygen concentration during the heat treatment step and the cooling treatment step according to claim 1 is 500 ppm or less.   2. The electronic component thermal screening method according to claim 1, wherein the surface temperature of the electronic component during the heat treatment is 210 to 280 [deg.] C.

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