JP3882362B2 - Test piece for solderability evaluation and printed wiring board having the same - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention includes a test piece for evaluating solderability and a test coupon for evaluating solderability for objectively and quantitatively determining the quality of solderability of a printed wiring board (printed board). The present invention relates to a printed wiring board.
[0002]
[Prior art]
For printed wiring boards, surface treatment (rosin-based preflux treatment, gold plating) is used to prevent oxidative deterioration of conductor patterns (land, through-holes, etc.) provided on the surface and maintain good solderability. , Solder coating, water-soluble preflux treatment (alkyl benzimidazole = copper complex formation), etc.), but these surface treatments may deteriorate or fail to adversely affect the solderability of the conductor pattern. .
[0003]
Therefore, in order to evaluate the solderability of a printed wiring board that depends on the quality and deterioration of such surface treatment (deterioration with time, high temperature deterioration, high humidity deterioration, etc.), conventionally, (1) The solder paste printed on the print is heated in a reflow oven (reflow soldering) and melted to measure the wetted area of the adhered solder (solder spreadability measurement), or (2) reflow soldering is performed The method of measuring the solder rising height in the through hole (measurement of soldering up) has been employed (see JIS C5013 / 5014).
[0004]
However, in these methods, a destructive test is performed using an alternative printed wiring board for testing, and in addition, since the evaluation of the test result is performed visually, there are many parts that depend on the subjective evaluation, and the evaluation result is actually There is a problem that the result of the solderability of the printed wiring board is not sufficiently expressed. Another problem is that the measurement is not easy because it is necessary to use an actual soldering apparatus.
[0005]
For this reason, it has been difficult for the conventional methods (1) and (2) to easily and quantitatively evaluate the solderability of the printed wiring board. In particular, considering the current situation where higher density mounting is required with the development of digital technology in recent years, an objective and quantitative evaluation method for the solderability of printed wiring boards can be quickly established. It has been requested.
[0006]
Recently, the present inventors have evaluated the reflow solderability of printed wiring boards by the solder paste wetting balance method (hereinafter referred to as reflow soldering method), An apparatus (reflow soldering tester) for carrying out the method was proposed (Journal of Circuit Packaging Society, 13 (2), 109 to 114 (1998)). FIG. 5 shows a schematic diagram of the reflow soldering tester. This device is a device for measuring the solder wetting time by measuring the time change of the force acting on the test piece.
[0007]
By the way, in order to ensure good solderability, it is necessary that the solder be wet. Here, the wetting of the solder can be measured by the time change of the force acting on the test piece. When the solder wetness is poor, the surface tension is shown in FIG. 6 (solder wetting curve (change in force applied to the test piece over time), P ₁ = heating start point; P ₂ = zero cross point; time from P _{1 to} P ₂ It acts downward (repulsive force) in (t ₀ ) = wetting time (zero crossing time)), and acts upward (tension) when wetting is improved. Therefore, the solderability of parts and materials can be quantitatively evaluated using the wetting time as an index.
[0008]
In this reflow soldering method, a test piece 10 of a printed wiring board (a front conductor portion 2a and a back conductor portion 2b are formed in layers on one end of an insulating substrate 1 as solderability evaluation lands (see FIG. 4). )) Is put into the solder paste before melting, and then the solder paste is heated to melt. For this reason, the land of the test piece is also heated before the solder paste is completely melted, and the flux in the solder paste is activated, and the action removes oxide film and dirt, thereby cleaning the surface of the test piece. The
[0009]
On the other hand, when the test piece is suddenly immersed in the molten solder (in the case of the conventional wetting balance method), since the surface of the test piece is not cleaned, large buoyancy (negative surface tension) occurs first. As a result, the test piece is rejected and the surface tension cannot be measured.
[0010]
However, in the case of the reflow soldering method, the influence of buoyancy can be suppressed because the (positive) surface tension of the molten solder paste acts before the occurrence of buoyancy. Therefore, it is possible to measure the wettability (solderability) of the solder by measuring the time change of the force (surface tension and buoyancy) acting on the test piece when the solder paste is melted.
[0011]
Incidentally, the reflow soldering tester shown in FIG. 5 includes a micropot 52 filled with a solder paste 51, a heating bath 54 filled with a low melting point metal 53, and a load cell 55 (high sensitivity load sensor). Have.
[0012]
The micropot 52 is fixed at a predetermined position by a fixing jig 56. The low melting point metal 53 in the heating bath 54 is heated to a predetermined temperature by a temperature adjusting device 59 including a heater 57 and a temperature detecting device 58 and is in a molten state. The heating bath 54 and the fixing jig 56 can be moved in the vertical direction by the driving device 60.
[0013]
The load cell 55 is connected to an electromagnetic chuck mechanism 62 that holds a holder 61 for holding the test piece 10. Further, a recording device 63 for processing data obtained from the load cell 55 is connected.
[0014]
A control device 64 is provided between the recording device 63 and the drive device 60 for controlling them in an integrated manner.
[0015]
The operation of testing the solderability of the test piece 10 as shown in FIG. 4 with the reflow soldering tester having such a configuration will be described below.
[0016]
First, the test piece 10 is mounted on the holder 61, and then the micropot 52 is raised so that the front conductor portion 2 a and the back conductor portion 2 b of the test piece 10 are immersed in the solder paste 51, and the bottom surface in the micropot 52 And fixed with a predetermined gap between them.
[0017]
Next, the heating bath 54 containing the molten low melting point metal 53 is raised by the driving device 60, the liquid surface of the low melting point metal 53 is brought into contact with the micropot 52, and the solder paste 51 is heated for a predetermined time. With the start of heating, the load cell 55 detects the time change of the force (buoyancy and surface tension) acting on the test piece 10, and the data (voltage) output from this is recorded by the recording device 63. Then, since a graph as shown in FIG. 6 is obtained, a time t ₀ from the heating start point P ₁ to the zero cross point P ₂ is obtained and recorded as a wetting time. The shorter the wetting time, the better the solderability.
[0018]
[Problems to be solved by the invention]
However, when the test piece 10 having a structure as shown in FIG. 4 is used, the surface treatment of the conductor portions (2a, 2b) of the test piece 10 and the subsequent surface condition variation with time will occur. When such a variation occurs, when the relationship between the heating time and the output of the load cell 55 is plotted in the figure, a step-like wetting curve as shown in FIG. 6 is shown. The cause of showing such a step-like wetting curve may be due to day wetting or the like, and it is substantially difficult to determine accurate solderability. Moreover, the reproducibility is not sufficient. Furthermore, it is difficult to separately distinguish the solderability of the front conductor portion 2a and the solderability of the back conductor portion 2b.
[0019]
The present invention is intended to solve the above-described problems of the conventional technique, and uses a reflow soldering tester capable of simply and objectively and quantitatively evaluating the solderability of a printed wiring board. In some cases, the object is not to show a staircase-like wetting curve and to reliably identify the solderability of the front and back surfaces.
[0020]
[Means for Solving the Problems]
As a test piece for evaluating the solderability of a printed wiring board, the present inventors provide a surface conductor portion and a back conductor portion on one end and the other back end of the insulating substrate, respectively. Each backside solderability test can be performed separately, and the test piece can be easily divided by providing a dividing line for dividing the insulating substrate (preferably divided into two) into the central portion of the insulating substrate, and further identifying the front and back sides It was found that the front and back sides of the test piece after division can be identified by providing a marking area for the purpose, and the present invention has been completed.
[0021]
That is, according to the present invention, a surface conductor portion and / or a through hole and a back conductor portion and / or a through hole are provided at one end portion and the other end portion of the back surface of the insulating substrate, respectively. For the evaluation of solderability of a printed wiring board, wherein a dividing line is provided in the central part of the insulating substrate, and a marking area for identifying the back surface or for identifying the front surface is provided on the back surface or front surface of the insulating substrate Provide test pieces for use.
[0022]
In addition, the present invention provides a printed wiring board in which the above-described test piece for solderability evaluation can be separated as a test coupon for solderability evaluation at a position where the solderability of the printed wiring board can be represented. provide.
[0023]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail.
[0024]
FIG. 1 is a perspective view of a test piece for evaluating solderability of the present invention as viewed from the back side. This test piece 10 has a structure in which a surface conductor portion 2a is provided at one end portion of the surface of the insulating substrate 1, and a back conductor portion 2b is provided at the other end portion of the back surface. Thus, by providing the front conductor portion 2a and the back conductor portion 2b separately, it is possible to prevent a step-like wetting phenomenon due to variations in the surface state of the front and back surfaces, and more stability, reproducibility, and practicality. High quantitative data can be obtained.
[0025]
The formation of the front surface conductor portion 2a and the back surface conductor portion 2b can be performed by an ordinary printed wiring board manufacturing method (subtractive method, additive method, or the like).
[0026]
In addition, the test piece 10 is provided with a dividing line L for dividing the insulating substrate 1 into two at almost the center of the insulating substrate 1. The test piece 10 can be easily divided along the dividing line L without using a special device or the like. The divided test pieces 10 become a pair of test pieces for evaluating the solderability and the surface treatment state of the conductor portions 2a and 2b on the front and back surfaces of the printed wiring board.
[0027]
The dividing line L may be a V cut line or a perforation as shown in FIG. 1 and FIG. 2 described later. Here, the V cut line can be formed by a cutting machine, and the perforation can be formed by an NC drill or a die press.
[0028]
Further, in this test piece 10, marking areas 3 a (for example, copper foil patterns), 3 b (pits) for identifying the front and back surfaces are provided on one surface of the insulating substrate 1, but are not limited thereto. That is, the marking area may be provided so that the two test piece pieces can be distinguished when the test piece 10 is divided into two. Therefore, it is not necessary to provide both the marking areas 3a and 3b at the same time, and only one of them may be provided.
[0029]
Such a marking region can be formed by a method of patterning a copper foil into a dot shape or a method by mechanical processing (such as a scratch or a pit).
[0030]
As shown in FIG. 2A (plan view) and FIG. 2B (cross-sectional view), the test piece 10 for evaluating solderability of the present invention is provided between the front conductor portion 2a and the back conductor portion 2b. A through hole Th may be provided. In this case, the through hole Th may be provided only at one end of the test piece. Further, two or more through holes Th may be provided at both ends of the test piece, and the front surface conductor portion 2a and the back surface conductor portion 2b are not necessarily formed.
[0031]
In order to obtain data with good stability and reproducibility, one through hole is desirable at one end, and it is desirable not to form a surface conductor portion. Alternatively, only the through hole may be provided at one end, and only the front conductor portion or the rear conductor portion may be provided at the other end.
[0032]
In order to match the solderability evaluation result of the test piece 10 for solderability evaluation of the present invention with the reproducibility of the actual solderability evaluation result of the printed wiring board, the solderability of the printed wiring board is representative. It is preferable to provide the test piece 10 for evaluating solderability of the present invention in a separable manner as a test coupon at a position to be obtained (for example, center, four corners, opposite sides, diagonal positions, etc.). Thereby, the test coupon by which the same process as the surface treatment of the actual printed wiring board was performed can be obtained. Therefore, when the solderability of the test coupon is evaluated, the solderability of the printed wiring board and its distribution are substantially evaluated by nondestructive inspection.
[0033]
Here, as a position that can represent the solderability of the printed wiring board, as shown in a set of four printed wiring boards in FIG. 3A, a “discarded printed wiring board region” R that is cut off during assembly. Can be mentioned.
[0034]
Further, in the case of a printed wiring board in which the discarded printed wiring board region R does not exist, the test piece 10 for solderability evaluation may be incorporated as a test coupon in a separable manner at the peripheral edge or the center thereof. In a printed wiring board having no discarded printed wiring board area, a test coupon for solderability evaluation may be installed in an empty space (such as a ground portion) of the printed wiring board. If the printed wiring board has no empty space, a test coupon installation area may be provided separately.
[0035]
As a method for providing the test piece 10 for solderability evaluation in a separable manner on the printed wiring board, as shown in FIG. 3 (b) which is a partially enlarged sectional view of the area A in FIG. 3 (a), the discarded printed wiring board The cut line CL, which is the boundary line between the region R and the printed wiring board P, is used as a V cut line VL, or as shown in FIG. 3C, which is a partially enlarged plan view of the B region in FIG. The eye M may be used. Further, as shown in FIG. 3D, which is a partially enlarged plan view of the C region in FIG. 3A, a groove G is formed around the periphery while providing a hold region H that is partially discarded and is continuous with the printed wiring board region R. It may be provided. Here, the groove G can be formed at the same time when the printed wiring board is processed (outer shape processing, drilling step) by NC router processing or a die press. In view of workability, the mode of FIG.
[0036]
The test piece for evaluating solderability of the present invention described above is very suitable as a test sample for a reflow soldering tester as shown in FIG.
[0037]
【The invention's effect】
According to the test piece for solderability evaluation of the present invention, when a reflow soldering tester capable of simply and objectively and quantitatively evaluating solderability is used, a step-like wetting curve is not shown. Moreover, the solderability of the front and back surfaces of the printed wiring board can be reliably identified.
[0038]
In addition, according to the printed wiring board provided with the test piece for solderability evaluation of the present invention as a test coupon for solderability evaluation, the solderability is quantitatively evaluated before soldering to the printed wiring board in an actual process. can do. Therefore, it is possible to perform an acceptance inspection of the printed wiring board and an inspection of the storage state (deterioration after storage), and it is possible to prevent the occurrence of defective soldering in the circuit mounting process. Also, when a soldering failure occurs in the circuit mounting process of a printed wiring board, the location of the cause of the failure (that is, whether it is a printed wiring board, component, solder, post flux, soldering process (process Can be easily identified. In addition, the development process of the surface treatment agent for the printed wiring board, the quality performance check, the process management, and the shipping inspection at the manufacturing factory and the plating factory of the printed wiring board can be easily performed.
[Brief description of the drawings]
FIG. 1 is a lower perspective view of a test piece for evaluating solderability of the present invention.
FIG. 2 is a plan view (FIG. 2A) and a cross-sectional view (FIG. 2B) of a test piece for evaluating solderability according to another embodiment of the present invention.
FIG. 3 is a plan view of the printed wiring board provided with the test piece for solderability evaluation of the present invention as a test coupon (FIG. 3A), and a partially enlarged sectional view of the region A (FIG. 3B). FIG. 4B is a partially enlarged plan view of the B region (FIG. 3C) and a partially enlarged plan view of the C region (FIG. 4D).
FIG. 4 is a cross-sectional view of a conventional test piece for solderability evaluation.
FIG. 5 is a schematic diagram of a reflow soldering tester.
FIG. 6 is a solder wetting curve obtained when a conventional test piece for evaluating solderability is used.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Insulation board | substrate, 2a Front surface conductor part, 2b Back surface conductor part, 3a, 3b Marking area | region 10 Test piece for solderability evaluation, L dividing line, CL cutting line, P printed wiring board, R discard printed wiring board area | region, Th Through hole

Claims (4)

A front conductor portion and / or a through hole and a back conductor portion and / or a through hole are provided at one end of the front surface and the other end of the back surface of the insulating substrate, respectively, and the dividing lines for dividing the insulating substrate are insulated. A test piece for evaluating solderability of a printed wiring board, wherein the test piece is provided on a substrate, and a marking region for identifying the back surface or for identifying the front surface is provided on the back surface or the front surface of the insulating substrate. A printed wiring board in which the test piece for solderability evaluation according to claim 1 is detachably provided as a test coupon for solderability evaluation at a position that can represent the solderability of the printed wiring board. The printed wiring board according to claim 2, wherein the test coupon for solderability evaluation is provided in a discarded printed wiring board region that is cut off during assembly. The printed wiring board according to claim 2, wherein the printed wiring board is discarded and does not have a printed wiring board area, and a test coupon for solderability evaluation is provided at a peripheral edge portion or a component non-mounting portion.

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