Background technology
Along with on the market electronic product being wanted light, thin, short, little demand, in the design of semiconductor chip,, put into more electronic component at the semiconductor substrate of limited area; This measure makes that promptly the distribution density of the contact that semiconductor chip and/or its packaging body are external increases, pitch smaller.Particularly docking point spacing less (for example below 0.5mm (containing)), with the semiconductor package body of BGA encapsulation, when it was assembled in circuit board, the degree of difficulty that above-mentioned semiconductor package body is aimed at circuit board was big especially; Though have with the spherical contact of scolder (solder) (industry common name " tin ball (solder ball) ") of the semiconductor package body of BGA encapsulation and can aim at voluntarily and the characteristic of correcting, the bigger departure of tolerable when assembling, but permissible deviation range is successively decreased along with the minimizing of above-mentioned spherical contact spacing; Especially above-mentioned spherical contact spacing be reduced to that for example 0.5mm (containing) is following the time, aim at not good easily at above-mentioned semiconductor package body and circuit board.And through after the step of reflow, solder bonds thing (solder joint) open circuit and/or problem of short-circuit take place easily, and make the foregoing circuit plate must reform (rework) or scrap, production process yield and cost are all caused harmful effect; Even above-mentioned solder bonds thing open circuit and problem of short-circuit fortunately do not take place, the quality of above-mentioned solder bonds thing also might be affected, the area of actual engagement reduces and can't present desirable lantern shape, solder bonds thing outside particularly healing, it is bigger to punctual departure, and it is also bigger to make it engage the suffered influence of quality, electronic product after the assembling is in transportation simultaneously, store, during with use, more the suffered external stress of the solder bonds thing in the outside is also bigger, thereby quicken the fatigue fracture of the solder bonds thing in the outside, and the reliability of the electronic product assembled is caused harmful effect.
Figure 1A shows the vertical view of a printed circuit board (PCB) 100.Printed circuit board (PCB) 100 has a welding resisting layer (solder mask) 105 on surface thereof, the opening 102 that welding resisting layer 105 has a plurality of wide W, arranges with spacing (pitch) P, expose a plurality of weld pads 103 and a plurality of weld pads 104 that are positioned at the perimeter that are positioned at interior zone, wherein W<P, and spacing P is the distance of the geometric center point of adjacent two openings 102.Wherein, weld pad 104 is the outside that is arranged in weld pad 103, and weld pad 103 is to be arranged in delegation among Figure 1A; And weld pad 104 is two outsides that are arranged in weld pad 103, is discontinuous two single files.Weld pad 103 and 104 can be the weld pad of SMD (solder mask define) type weld pad, NSMD (non-solder mask define) type weld pad, SMD-NSMD mixed type weld pad or other patterns.With the scope that rises of dotted line 106 frames of sealing is follow-up when an electronic component is assembled in printed circuit board (PCB) 100, the precalculated position of this electronic component.Please refer to Figure 1B, it is a vertical view, system shows known frock appliance 150, applicable to a paste with scolder (for example being leypewter, leaded kamash alloy or lead-free kamash alloy) and/or scaling powder (industry is commonly called as " tin cream ", below also claim) being formed at printed circuit board (PCB) 100 with stencil methods (stencil printing).Frock appliance 150 cordings have the metallic plate of a set thickness, have a plurality of openings 151, and these opening 151 summarys are provided with according to the weld pad arrangement mode of printed circuit board (PCB) 100.Yet, when using frock appliance 150 that tin cream is formed at circuit board 100 surfaces, the slightly variant situation of each point tin cream adhesion amount may appear.When the spherical contact of the scolder of tin cream and semiconductor package body merges, the long-pending difference that also therefore produces of formed solder bonds object.
Fig. 2 A system shows a kind of situation of above-mentioned difference, and certain any solder bonds object is long-pending big especially, and be very easy to because of be in contact with one another bridge joint take place between the adjacent solder bonds thing this moment.Fig. 2 B then is the another kind of situation that shows above-mentioned difference, and the solder bonds object that is positioned at the outside is long-pending less, and the probability that empty weldering takes place this moment just can be higher, and the electrically connect between can't effective constitution two relative weld pads; Even and form effective solder bonds thing, its actual bonding area is too small because the contact in the outside more often bears the external force effect, may take place bond strength not enough and to circuit board assembly structure 1 ' with 1 " reliability cause harmful effect.
Summary of the invention
In view of this, main purpose of the present invention is that a kind of circuit board assembling method and structure are provided, in the bigger departure of when assembling tolerable, the intensity of solder bonds thing that can also the reinforcement outside is to promote process rate, reduce the processing procedure cost and to increase production reliability.
Another object of the present invention provides a kind of frock appliance, be applicable to a paste that has a scolder and/or a scaling powder at least is formed on the circuit board, thereby make the circuit board assembly structure of the invention described above, to promote process rate, reduce the processing procedure cost and to increase production reliability.
For reaching above-mentioned purpose of the present invention, the present invention system provides a kind of circuit board assembly structure, comprise: a printed circuit board (PCB), has a welding resisting layer on a surface, the opening that above-mentioned welding resisting layer has a plurality of wide W, arranges with spacing (pitch) P, expose at least one first weld pad and a plurality of second weld pad, wherein second weld pad system is arranged in the outside of first weld pad; At least one first solder bonds thing (solder joint) is electrically connected on above-mentioned first weld pad, and the above-mentioned first solder bonds thing has a Breadth Maximum J1; A plurality of second solder bonds things are electrically connected at respectively on above-mentioned second weld pad, and the above-mentioned second solder bonds thing has a Breadth Maximum J2 respectively, and J1<J2; And an electronic component, have the 3rd identical substantially weld pad of a plurality of arrangement modes and above-mentioned opening, be electrically connected at above-mentioned first solder bonds thing and the above-mentioned second solder bonds thing respectively.
The present invention system provides a kind of frock appliance again, be applicable to a paste that has a scolder and/or a scaling powder at least is formed on the circuit board, comprise: one has the metallic plate of set thickness, weld pad arrangement mode according to above-mentioned printed circuit board (PCB), be provided with at least one first opening and a plurality of second opening, the area of wherein above-mentioned second opening is greater than the area of above-mentioned first opening, and above-mentioned second opening system is arranged in the outside of above-mentioned first opening.
For further specifying above-mentioned purpose of the present invention, design feature and effect, the present invention is described in detail below with reference to accompanying drawing.
Description of drawings
Figure 1A is the vertical view of a printed circuit board (PCB).
Figure 1B is the vertical view of an existing frock appliance.
Fig. 2 A is a profile, shows that existing circuit board assembly structure ' because of certain any solder bonds object is long-pending makes between the adjacent solder bonds thing especially greatly to be very easy to because of being in contact with one another the problem that bridge joint takes place.
Fig. 2 B is a profile, shows that the solder bonds object in existing circuit board assembly structure ' the be positioned at outside is long-pending less, and the probability that empty weldering takes place this moment just can be higher, and the problem of the electrically connect between can't effective constitution two relative weld pads.
Fig. 3 is the profile of a circuit board assembly structure of the present invention.
Fig. 4 is for showing the schematic diagram of opening shape possible on the frock appliance.
Fig. 5 A is the vertical view of an embodiment of demonstration frock appliance of the present invention.
Fig. 5 B is a schematic diagram, shows the position relation of the 3rd opening and the corresponding weld pad in the upper left corner that is positioned at Fig. 5 A.
Fig. 6 is a profile, shows in the assembling process of circuit board assembly structure of the present invention the step that frock appliance is aimed at printed circuit board (PCB).
Fig. 7 is a profile, shows in the assembling process of circuit board assembly structure of the present invention, forms the step of tin cream on printed circuit board (PCB).
Fig. 8 is a vertical view, shows the advantage that circuit board assembly structure of the present invention is had in assembling process.
Fig. 9 is along the profile of AA line among Fig. 8.
Figure 10 A is a profile, shows the state of the second solder bonds thing of the present invention when reflow process.
Figure 10 B is a profile, shows the state of the first solder bonds thing of the present invention when reflow process.
Figure 11 is a vertical view, shows the employed printed circuit board (PCB) of second embodiment of the invention.
Figure 12 is a vertical view, shows the employed frock appliance of second embodiment of the invention.
Figure 13 is a profile, shows the circuit board assembly structure of second embodiment of the invention.
Figure 14 A is a microphotograph, is shown as the solder bonds thing that Figure 13 is denoted as (C).
Figure 14 B is a microphotograph, is shown as the solder bonds thing that Figure 13 is denoted as (D).
Figure 15 shows the suffered stress distribution schematic diagram of electronic component when reflow.
Embodiment
Please refer to Fig. 3, circuit board assembly structure 1 provided by the present invention comprises: a circuit board 100, has a welding resisting layer 105 on a surface, the opening 102 that above-mentioned welding resisting layer has a plurality of wide W, arranges with spacing (pitch) P, expose first weld pad 103 and a plurality of second weld pads 104, wherein second weld pad 104 is arranged in the outside of first weld pad 104; At least one first solder bonds thing (solder joint) 61 is electrically connected on above-mentioned first weld pad 103, and the above-mentioned first solder bonds thing 61 has a Breadth Maximum J1; A plurality of second solder bonds things 62 are electrically connected at respectively on above-mentioned second weld pad 104, and the above-mentioned second solder bonds thing 62 has a Breadth Maximum J2 respectively, and J1<J2; And an electronic component 10, have a plurality of arrangement modes three weld pad 12 identical substantially with above-mentioned opening, be electrically connected at the above-mentioned first solder bonds thing 61 and the above-mentioned second solder bonds thing 62 respectively.Be not easy take place bridge joint phenomenon because the adjacent first solder bonds thing 61 and the spacing between the second solder bonds thing 62 are big than the equivalence element shown in Fig. 2 A this moment.In addition, because it is bigger to be positioned at the second solder bonds thing, 62 width in the outside, its actual bonding area increases, and can effectively keep bond strength, improves the reliability of circuit board assembly structure 1.
Control the width of solder bonds thing, an embodiment of the present invention reaches by the amount that control is attached to the tin cream on the circuit board 100.Please refer to Fig. 4, the opening on traditional frock appliance is the circular open as opening a.At width is under the situation of W, and its aperture area is π W
2/ 4.Under the situation that does not change the W value, for increasing aperture area, can adopt the rectangular aperture as opening b to increase the adhesion amount of tin cream, the aperture area of this moment is W
2But because the situation of tin cream accumulation may appear in four corners of rectangular aperture, cause the puzzlement on the production process, so the present invention designs the rectangular aperture with arc chord angle as opening c especially, is used on the frock appliance, the aperture area of opening c is between π W
2/ 4 and W
2Between.By the size of adjusting arc chord angle, can adjust the aperture area of rectangular aperture.Certainly, still there are other modes may be able to solve the tin cream accumulation problem of rectangular aperture, for example four corners of rectangular aperture taked rescinded angle to handle, form an octangle opening.In addition, if do not consider to increase under the situation that A/F can reduce the distance between two openings (and formed tin cream), can also adopt the circular open of big width.
Next please refer to Fig. 5 B, show an embodiment of frock appliance of the present invention.Wherein frock appliance 300 is to be used for tin cream is formed on the circuit board 100 of Figure 1A.Frock appliance 300 has the metallic plate 305 of a set thickness, arrangement mode according to weld pad on the circuit board 100, be provided with first opening 301 and a plurality of second openings 302, wherein the area of each second opening 302 is greater than the area of each first opening 301, and second opening 302 is arranged in the outside of first opening 301; That is, first opening 301 is the positions with respect to the weld pad 103 of printed circuit board (PCB) 100, be used for above-mentioned tin cream is formed at weld pad 103, and second opening 302 is the positions with respect to the weld pad 104 of printed circuit board (PCB) 100, is used for above-mentioned tin cream is formed at weld pad 104.
Consider in the process with electronic component 10 circuit board assembly structure 1 of formation Fig. 3 with printed circuit board (PCB) 100 assemblings; especially when the step of reflow (reflow); the corner portions located of electronic component 10 can be subjected to bigger deflection usually, and the solder bonds thing 61/62 generation bridge joint that the solder bonds thing 62 of the weld pad 12 that makes the corner portions located that connects electronic component 10 and the weld pad 104 of printed circuit board (PCB) 100 is easier to and be close to.Situation for fear of above-mentioned bridge joint takes place, present embodiment also designs frock appliance 300 and has the 3rd opening 303 that is positioned at the corner, it is with respect to the weld pad 104 in four corners of printed circuit board (PCB) 100 position in the outside slightly, is used for above-mentioned tin cream is formed at the weld pad 104 in four corners.Fig. 5 B is the position relation that is used for illustrating the 3rd opening 303 with the corresponding weld pad 104 in the upper left corner that is positioned at Fig. 5 B.The central point 502 of the upper left corner the 3rd opening 303 is that the central point 501 with respect to weld pad 104 carries out displacement towards the upper left side.For example, if opening 303 width are 12mil, then displacement can be 2mil.In the case, the tin cream 50 formation positions of prediction also can be offset to the upper left side with respect to weld pad 104.The 3rd opening 303 in other corners then is to carry out displacement towards deep direction.
When the step on the circuit board 100 that carries out scolder is formed at Figure 1A, at first frock appliance 300 is covered on the relative position of circuit board 100, as shown in Figure 6.Frock appliance 300 among Fig. 6 is to be profiles along the line segment AA of Figure 1A along the profile of the line segment BB of Fig. 5 B, circuit board 100.Then tin cream is formed on circuit board 100 surfaces with stencil methods.
Please refer to Fig. 7, show the profile that tin cream 50 has been formed on the circuit board 100.Because the aperture area of the 3rd opening 303 is greater than the area of first opening 301, the amount that is formed at the tin cream 50 on the weld pad 104 is many than the amount of the tin cream on the weld pad 103 50, and two weld pads 104 among Fig. 7 just in time are positioned at corner, so the also skew laterally of the position of formed tin cream 50.
Next please refer to Fig. 8 and Fig. 9, electronic component 10 is placed on the circuit board 100,, electronic component 10 is formed with circuit board 100 electrically connect, and constitute circuit board assembly structure of the present invention 1 shown in Figure 3 again via the step of reflow (reflow).Wherein, electronic component 10 is preferably semiconductor package body, the semiconductor package body of wafer-level package, the semiconductor chip that covers crystalline form or the connector with the BGA encapsulation.It has a plurality of solder projections 13 usually before being assembled in circuit board 100, be electrically connected at a plurality of arrangement modes and weld pad 103 and 104 respectively substantially on the corresponding weld pad 12, and the width of each solder projection 13 (or diameter), height equidimension are all roughly the same.And in Fig. 9, each solder projection 13 is to place respectively on the corresponding tin cream 50.
If in the process of Fig. 8 and manufacturing circuit board assembly structure 1 shown in Figure 9, the position of electronic component 10 is because the location is inaccurate or machine error and to the skew of the upper right corner of drawing (tram is represented with the dotted line scope 106 of Fig. 8).This moment, the profile along the AA line was to be illustrated among Fig. 9.
As mentioned before, the contact spacing very hour, the degree of difficulty of aiming at during the circuit board assembling is big especially.At this moment, adopt circuit board assembling method of the present invention also can have the function of automatic homing.In Fig. 9, the amount of the tin cream 50 because the amount of the tin cream 50 on the weld pad 104 of both sides is big on the weld pad 103 is less, therefore in reflow process, can form the first solder bonds thing 61 shown in similar Fig. 2 C and the structure of the second solder bonds thing 62, but solder bonds thing 61 and 62 all is in the melting state at this moment.What Figure 10 A showed is the schematic diagram of the second solder bonds thing 62, and dotted line r represents the position of an imaginary circles spheroid among the figure.Can learn that from basic physics because the effect of cohesive force, the second solder bonds thing 62 that is in the melting state has a trend that contracts in imaginary circles spheroid r, thereby produce the upward act stress that makes progress shown in arrow among the figure.What Figure 10 B showed then is the schematic diagram of the first solder bonds thing 61, and dotted line r represents the position of an imaginary circles spheroid among the figure.Can learn that from basic physics because the effect of cohesive force, the first solder bonds thing 61 that is in the melting state has a trend of opening outside imaginary circles spheroid r, thereby produces a downward following tension stress.If do not have other external force effects, then descend the summation of tension stress and last act stress just can make electronic component 10 " floating " on circuit board 100.
Therefore in reflow process shown in Figure 9, the tin cream 50 of fusion just provides relative upward act stress with direction 71,73 to electronic component 10 with solder projection 13 on the weld pad 104 of both sides, the tin cream 50 of fusion on the weld pad 103 just provides the relative tension stress down with direction 72 to electronic component 10 with solder projection 13, thereby be easier to drive and impel electronic component 10 to move towards the direction of arrow 74, till electronic component 10 arrives both allocations of dotted lines 106 automatically.At last, the above-mentioned melting state solder bonds thing 61 and 62 that is in is solidified, finished circuit board assembly structure shown in Figure 31.Therefore, circuit board assembly structure 1 of the present invention is in the process of assembling, when aiming at electronic component 10 with printed circuit board (PCB) 100, the departure that tolerable is bigger, especially opening 102 spacing P when 0.5mm (containing) is following (that is spacing of weld pad 102/103), more can reduce effectively as not good because of aiming at as described in the prior art, and, solder bonds thing open circuit and/or problem of short-circuit take place easily through after the step of reflow.
In addition, the value of the ratio (J2/J1) of solder bonds thing 61 and 62 minutes other Breadth Maximum J1, J2 is preferably 1.05~1.50 among Fig. 3, can solder bonds thing 62 be enough to form the lantern shape and bigger bonding area is provided and the situation of bond strength under, can further reduce the probability of adjacent solder bonds thing 62 bridge joints again, with the making yield and the cost of better lifting circuit board assembly structure 1 of the present invention.
In addition, as described in prior art, the electronic product after the assembling in transportation, store, when using, more the suffered external stress of the solder bonds thing in the outside is also bigger.And in Fig. 9, because the amount of the tin cream 50 on the weld pad 104 of both sides is bigger, in the process of reflow, can also form lantern shape and the bigger solder bonds thing 62 (being illustrated in Fig. 3) of width jointly with the solder projection 13 on it, bigger bonding area and bond strength can be provided, be enough to bear circuit board assembly structure 1 of the present invention in transportation, store, suffered external stress when using.
Please refer to Figure 11, show the vertical view of the circuit board 200 in the second embodiment of the invention.The welding resisting layer of circuit board 200 (solder mask) 205, opening 202, weld pad 203, with weld pad 204, can be equivalent to respectively Figure 1A and circuit board that 1B illustrates 100 welding resisting layer 105, opening 102, weld pad 103, with weld pad 104, so detailed description no longer.Wherein, weld pad 203 is distributed in the scope that rises with dotted line 207 frames, and weld pad 204 is distributed in the scope between dotted line 206 and 207, promptly is distributed in the outside of weld pad 203.And dotted line 206 is the follow-up position that an electronic component is assembled in printed circuit board (PCB) 200.
Next please refer to Figure 12, is a vertical view, shows the frock appliance 400 of second embodiment of the invention, and wherein frock appliance 400 is in order to a tin cream is formed at printed circuit board (PCB) 200, thereby makes circuit board assembly structure 2 (with reference to Figure 13).The metallic plate 405 of frock appliance 400, first opening 401, with second opening 402, be the metallic plate 305 that is equivalent to Fig. 5 frock appliance that A illustrates 300 respectively, first opening 301, with second opening 302, so detailed description no longer.And be positioned at second opening 402 in four corners, and then be equivalent to the 3rd opening 303 of Fig. 5 A, all be offset laterally.
Next please refer to Figure 13, is a profile, shows the circuit board assembly structure 2 of second embodiment of the invention, and wherein the circuit board in the circuit board assembly structure 2 200 is in the vertical view of Figure 11, along the profile of BB line.The electronic component 20 of circuit board assembly structure 2, weld pad 22, solder bonds thing 81, with solder bonds thing 82, can be equivalent to respectively circuit board assembly structure that Fig. 3 illustrates 1 electronic component 10, weld pad 12, solder bonds thing 61, with solder bonds thing 62, so detailed description no longer.
Please refer to Figure 14 A and 14B, Figure 14 A is denoted as the microphotograph of the solder bonds thing 81 of (C), Figure 14 B is denoted as the solder bonds thing 82 of (D) for Figure 13 microphotograph for Figure 13.Wherein, the P of this moment be that the maximum gauge (Breadth Maximum in the photo) of about 0.5mm (500 μ m), solder bonds thing 81 is that the maximum gauge (Breadth Maximum in the photo) of about 333 μ m, solder bonds thing 82 is about 388 μ m, and the value of the ratio (J2/J1) of solder bonds thing 81 at this moment and 82 minutes other Breadth Maximum J1, J2 is about 1.17.This is for an example of practical application.Can learn that from figure the angle between solder bonds thing 81 and the weld pad 203 (fillet angle) R1 is greater than the angle R2 between solder bonds thing 82 and the weld pad 204.
Please refer to Figure 15, show the stress distribution schematic diagram that when reflow electronic component 20 is suffered.The solder bonds thing 81 that is positioned at inboard (scope that dotted line 207 frames rise) produces tension stress down, electronic component 20 (being considered as transparent) is drawn close to central authorities shown in arrow among the figure, be positioned in 82 generations of solder bonds thing in the outside and lift stress, with the weight of supporting electronic component 20 and electronic component 20 is swum on the circuit board 200.
Though the present invention describes with reference to above-mentioned specific embodiment, but those of ordinary skill in the art will be appreciated that, above embodiment is used for illustrating the present invention, under the situation that does not break away from spirit of the present invention, also can make the variation or the replacement of various equivalences, therefore, as long as in connotation scope of the present invention in the scope to the variation of the foregoing description, claims that modification all will drop on the application.