JP2011254034A - Flow soldering method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a flow soldering method capable of soldering a plurality of inserting and mounting electronic components having different thermal capacity and heat resistance, without losing characteristics, and with junction quality being assured.SOLUTION: The flow soldering method includes a tolerable range specification step for specifying a tolerable range of soldering condition based on solder-wet characteristic in a through hole as well as a temperature of a body part of an inserting and mounting electronic component, available from a combination of kind of a circuit board; thermal capacity and heat resistance of an inserting and mounting electronic component; kind of used solder; and soldering condition, and further a correlationship acquiring step for acquiring a correlationship between the thermal capacity and the tolerable range of soldering condition. It also includes a soldering condition deciding step for deciding a soldering condition from the correlationship.

Description

The present invention is a technique that is generally used in assembling electronic equipment, and is mounted on a circuit board or a module (multi-chip module) or the like, and is mounted and mounted electronic component (IMD) or surface mounted electronic component (SMD). The present invention relates to a flow soldering method for directly mounting (Surface Mount Device).

As a method for mounting an electronic component on a circuit board, several methods such as a flow soldering method and a reflow soldering method have been put into practical use.
When mounting an insertion mounting electronic component having a lead on a circuit board having lands and through holes, a flow soldering method is generally used in many cases. In this method, an insertion-mounted electronic component (hereinafter abbreviated as “electronic component” if no strictness is required) is placed on the circuit board with the leads inserted into the through holes of the circuit board. The lower surface of the circuit board is brought into contact with the jet solder, and the lead is soldered to the circuit board by the solder wetted between the through hole and the lead.
FIG. 4 shows a state in which the jet solder 3 sent from the solder tank (not shown) to the jet nozzle 2 and ejected upward is in contact with the lower surface (B surface in FIG. 4) 11 of the printed circuit board 1 as a circuit board. Is shown. Although the electronic components arranged on the printed circuit board 1 are not shown in FIG. 4, actually, the lead is inserted into the through hole from the upper surface (F surface in FIG. 4) 12 downward. ing.

 In flow soldering, soldering is performed with a temperature profile as shown in FIG. In the case of FIG. 5, the two jet nozzles are arranged in two stages, and the printed circuit board and the electronic components mounted thereon are heated from the B surface side of the printed circuit board during the preheating heating, and the two stages. It is soldered by contact with the jet solder and cooled by natural heat dissipation. The reason why the jet nozzles are arranged in two stages is not only to ensure sufficient solder wetting but also to reduce problems such as solder bridges. It is also practical when the jet nozzle has one stage.

In the above process, the B surface of the printed circuit board is directly heated by preheating or contact with jet solder, and the temperature is always higher than the F surface of the printed circuit board. In the preheating, the temperature of the B surface is also set below the melting point of the solder. The B surface peak temperature is the temperature of the jet solder that comes into contact. The F-plane peak temperature is set below the heat resistance temperature of the electronic component to be mounted.
There are many types of electronic components mounted on a circuit board, and a plurality of electronic components having different heat capacities and heat-resistant temperatures are generally mounted on circuit boards used in electronic devices. In addition, there are many types of circuit boards depending on differences in materials, thicknesses, and the like, and there are a wide variety of types and number of components to be arranged and arrangement positions. For this reason, even if flow soldering is performed under the same soldering conditions, a difference appears in the wet-up state of the solder in the through hole. FIG. 6 is a cross-sectional view of the through hole portion showing this state as a model. In the figure, the lead of the electronic component is not shown, but the lead actually passes through the through hole.

In the soldering process, first, the B-side land 14 and the tip of the electronic component lead are wetted by the solder 4, and then the solder 4 gets wet in the through hole 13, and in some cases, the solder is applied to the F-side land 15. spread. Regarding the solder wetting rate in the through-hole 13, there is an IEC standard, and a state where it is wetted to 75% or more of the height of the through-hole 13 is regarded as acceptable, and less than that is regarded as unacceptable. 6 (a) shows a rejected state with a solder wetting rate of less than 75%, FIG. 6 (b) shows a passing state with a solder wetting rate of 75% or more, and FIG. The solder has spread to the land 15 and shows a passing state with a solder wetting rate of 100% or more. The wetting rate is evaluated by appearance observation, X-ray observation, and cross-sectional observation.
As described above, since there are various types of circuit boards and electronic components mounted on them, even if soldering is performed under the same flow soldering conditions, some solder wetting conditions satisfy the acceptance criteria. Some of them do not meet the heat-resistant condition when trying to secure a sufficient solder wetting rate for all electronic components.

In the conventional technology, for solder that does not meet the acceptance criteria, the solder wetting state that satisfies the acceptance criteria in the correction process by local heating with soldering iron, light beam, hot air, laser light, etc. Secured. However, in this method, the correction process is an individual operation and requires extra man-hours, and the joining quality also varies.
As a soldering method that does not require such an individual correction process, Patent Document 1 discloses a method for setting a heating condition that satisfies a required temperature profile in a reflow soldering method. According to this, "Isotherm diagram showing temperature rise" of multiple parts with different heat capacities etc. are overlapped, "Area where solderability of parts is a problem" and "Area where heat resistance of parts is a problem" Are set, and “a heating condition in which all of the objects to be heated satisfy a predetermined temperature profile” is set.

JP 2007-93031 A

The above-mentioned Patent Document 1 is intended to solder a plurality of electronic parts having different heat capacities and heat resistances by using a reflow soldering method without deteriorating the characteristics and surely securing the bonding quality. It is.
On the other hand, an object of the present invention is a flow soldering method for mounting and soldering a plurality of insertion-mounting electronic components including those having different heat capacities and heat resistances on the same circuit board and reliably and without impairing the characteristics of the electronic components. It is intended to ensure soldering quality and solder.

According to the first aspect of the present invention, when an insertion mounting electronic component having a lead is mounted on a circuit board having a land and a through hole, the insertion mounting electronic component is placed in the through hole of the circuit board and the lead is placed on the upper surface of the circuit board. Place the circuit board in the state where it is inserted from the side to the bottom side, and contact the bottom surface of the circuit board in this state with the molten solder ejected upward, and solder the lands and through holes of the circuit board and the leads inserted into the through holes. A soldering method of solder in a through-hole obtained by a combination of the type of the circuit board, the heat capacity and heat-resistant temperature of the insertion mounted electronic component, the type of solder used, and the soldering conditions And the tolerance specification process to identify the tolerance range of the soldering conditions based on the temperature of the body part of the insertion mounted electronic component In addition, using the allowable range of soldering conditions obtained in this process, the heat capacity and solder of the insertion mounted electronic component for each insertion mounted electronic component having the same heat-resistant temperature corresponding to the type of circuit board and the type of solder A correlation acquisition step of acquiring a correlation with the allowable range of the soldering conditions, and determining a soldering condition of the circuit board and insertion mounting electronic component to be subjected to flow soldering based on the correlation obtained in this step And a soldering condition determining step.

Since the correlation between the heat capacity of insertion-mounted electronic components and the allowable range of soldering conditions is acquired and the soldering conditions are determined based on that, the correlation between the insertion-mounting electronic components of any heat capacity The allowable range of soldering conditions can be grasped.
It should be noted that the accuracy of the obtained correlation will be higher if the allowable range specifying step is executed including the assumed maximum and minimum heat capacity insertion-mounted electronic components.
Further, as in the invention of claim 2, in the flow soldering method according to claim 1, the soldering condition is from when the lower surface of the circuit board starts to contact the molten solder to when the contact ends. It can be the joining time.

In the invention of claim 1, since the correlation between the heat capacity of the insertion mounted electronic component and the allowable range of the soldering conditions is obtained and the soldering conditions are determined based on the correlation, On the other hand, the allowable range of the soldering conditions can be grasped from the correlation.
Therefore, according to the present invention, even when a plurality of insertion-mounting electronic components including those having different heat capacities and heat resistances are mounted on the same circuit board and soldered, the quality of the electronic components is not impaired and the bonding quality is ensured. Can be secured and soldered. This eliminates the need for a separate correction process using a soldering iron or the like, thereby improving tact time and improving productivity.
Further, as the soldering condition, for example, as in the invention of claim 2, the joining time from when the lower surface of the circuit board starts to contact the molten solder to when the contact ends can be targeted.

Process drawing for explaining the characteristics of the flow soldering method according to the present invention FIG. 6 is a correlation diagram showing the correlation between the heat capacity of an insertion mounted electronic component and the joining time for explaining an embodiment of the flow soldering method according to the present invention. Flow diagram showing the data acquisition process for creating the correlation diagram in Figure 2 Conceptual diagram showing the main parts of the flow soldering method Temperature profile in flow soldering method Cross-sectional view of the through-hole part for explaining pass / fail judgment of the solder wet-up state

According to the flow soldering method of the present invention, an insertion mounting electronic component having a lead is mounted on a circuit board having a land and a through hole, and the correlation between the heat capacity of the insertion mounting electronic component and the allowable range of the soldering conditions. The feature is to acquire the relationship and determine the soldering conditions based on it. The three processes shown in FIG. 1 are “the soldering condition tolerance range specifying process”, “correlation acquiring process” and “soldering condition determination”. Process ".
In the "Soldering condition tolerance process", the solder wetting in the through hole is obtained by the combination of the circuit board type, the heat capacity and heat resistance temperature of the mounted electronic components, the type of solder used, and the soldering conditions. Based on the characteristics and the temperature of the main body of the insertion mounting electronic component, the allowable range of the soldering conditions is specified. In the "correlation acquisition process", using the allowable range of the soldering conditions obtained in the previous process, insertion mounting is performed for each electronic component that has the same heat-resistant temperature, corresponding to the type of circuit board and the type of solder. Obtain the correlation between the heat capacity of the electronic component and the allowable range of the soldering conditions. In the “soldering condition determination step”, the soldering conditions for the circuit board and the insertion mounted electronic component to be subjected to flow soldering are determined based on the correlation obtained in the previous step.
Since the correlation between the heat capacity and the allowable range of the soldering condition is obtained, the allowable range of the soldering condition for the electronic component having any heat capacity can be grasped from the correlation.
In the following, embodiments will be described using examples.

FIG. 2 is a correlation diagram showing the correlation between the heat capacity of the insertion mounted electronic component and the joining time for explaining an embodiment of the flow soldering method according to the present invention, and FIG. 3 creates the correlation diagram of FIG. 2 is a flow diagram showing a data acquisition process for
As shown in FIG. 5, the bonding time starts contact with the molten solder (jet solder 3 in FIG. 4) from which the lower surface of the printed circuit board (B surface 11 of the printed circuit board 1 in FIG. 4) is ejected upward. It is the time from contact to end of contact.
First, as an “acceptable range identification process for soldering conditions”, three types of insertion-mounted electronic components with the same heat resistance are mounted on the printed circuit board with heat capacities of 6.8 mJ / K, 17.2 mJ / K and 75.7 mJ / K, respectively. Then, a tin-silver-copper-based lead-free solder was used, and the flow soldering was repeated by changing the joining time from a short time to a long time using a temperature profile similar to FIG. At this time, the maximum temperature of the main part of the electronic component is measured for each flow soldering, the solder wetting rate is evaluated after the soldering is completed, and the heat resistance is confirmed by the presence or absence of changes in the characteristics of the electronic component. did.

The jet solder temperature corresponds to the B surface peak temperature in FIG. 5 and is usually set to the melting point of solder + 25 ° C.
The above process is summarized as the flow diagram of FIG. The lower limit value of the joining time is determined when the wetting rate satisfies the standard, and the upper limit value of the joining time is determined when the temperature of the main body reaches the heat-resistant temperature or when a characteristic change appears.
FIG. 2 shows the results obtained as described above, and the hatched portion indicates the allowable joining time range.
If such a diagram is created for each insertion / mounting electronic component with different heat resistance, the allowable bonding time can be ascertained for any mounting / mounting electronic component having any heat capacity. Can be secured.
This embodiment relates to the joining time among the soldering conditions, but it goes without saying that the correlation can be obtained in a similar manner with respect to other soldering conditions.

1 Printed circuit board
11 B side 12 F side 13 Through hole
14 B side land 15 F side land 2 Jet nozzle 3 Jet solder 4 Solder

Claims (2)

When mounting an insertion mounting electronic component having a lead on a circuit board having a land and a through hole, the insertion mounting electronic component is inserted into the through hole of the circuit board from the upper surface side to the lower surface side of the circuit board. In this flow soldering method, the lower surface of the circuit board in this state is brought into contact with the molten solder ejected upward, and the lands and through holes of the circuit board and the leads inserted into the through holes are soldered. And
The wetting characteristics of the solder in the through hole and the main body of the insertion mounting electronic component obtained by the combination of the type of the circuit board, the heat capacity and heat resistant temperature of the insertion mounting electronic component, the type of solder used and the soldering conditions An acceptable range identifying step for identifying an acceptable range of soldering conditions based on the temperature; and
Using the allowable range of the soldering conditions obtained in this process, the heat capacity and soldering conditions of the insertion mounted electronic components for each insertion mounted electronic component having the same heat resistance temperature corresponding to the type of circuit board and the type of solder A correlation acquisition step of acquiring a correlation with an allowable range of
A soldering condition determining step for determining a soldering condition of the circuit board and the insertion mounting electronic component to be subjected to flow soldering based on the correlation obtained in this step;
Having
A flow soldering method characterized by that. In the flow soldering method according to claim 1,
The flow soldering method, wherein the soldering condition is a joining time from the start of contact of the lower surface of the circuit board to the molten solder to the end of contact.

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