Encapsulation led quality of welding spot detection means and method
Technical field
The present invention relates to a kind of led field tests, particularly to a kind of encapsulation led quality of welding spot detection means and method.
Background technology
Light emitting diode (light emitting diode, led) is due to energy-saving and environmental protection, fast response time, cold light source etc.
Feature, is widely used in Landscape Lighting, backlight, street lamp and room lighting, is preferable alternative source of light.Led lamp beads are by chip, gold
Line, support and epoxy encapsulation composition, chip is welded on support by gold thread, realizes being electrically connected, welding quality good
Bad, it is directly connected to the life-span of led.In microelectronics Packaging, it is mutual by chip that the inefficacy of semiconductor device there are about 1/4~1/3
Even cause it is therefore necessary to detect to led welding quality.Common led quality of welding spot problem is mainly manifested in failure welding
The defects such as (rosin joint), soldered ball are excessive, solder joint Microfocus X-ray tube, the bonding wire all for led before encapsulation for the existing led quality of welding spot detection method
Processing quality is detected, to reject bonding wire defective product in time, it is to avoid enters encapsulation link and produces irremediable wave
Take.And in encapsulation process, packaging technology itself may produce impact, heat effect during led work etc. by welding quality
Factor is likely to affect welding quality, even results in the inefficacy of product when serious.Due to there being the parcel of encapsulated layer, for encapsulation
Led Welding quality test afterwards, conventional way be using chemical reagent melt away outer layer encapsulating material again by micro- sem observation, this
By the expendable damage of sample of unavoidable band.For realizing being analyzed to encapsulating led lamp beads interior welds quality, non-
Often it is necessary to develop a kind of lossless measurement analysis method.
Content of the invention
In consideration of it, a kind of it is an object of the invention to provide led quality of welding spot Non-Destructive Testing dress based on transient switching characteristics
Put and method, can achieve the judgement of quality of welding spot using this apparatus and method.Due to not needing the step corroding encapsulated layer, test
Process is quick, is especially advantageous for the welding procedure of encapsulating products is tested and analyzed.
The purpose of the present invention is realized by such technical scheme, encapsulates led quality of welding spot detection means, including electricity
Stream source, specimen holder, current measuring unit, photodetector, data collecting card and computer;On described driven with current sources specimen holder
Led work, the electric current of led switching moments is obtained by current measuring unit, and exports to computer;Described photodetector sets
Put the dead ahead in specimen holder, for gathering the optical signal that led sends and this optical signal being converted to the signal of telecommunication;Described smooth electrical resistivity survey
The outfan surveying device is connected with data collecting card, and data collecting card is connected with computer, and described data collecting card obtains light electrical resistivity survey
Survey the signal of telecommunication of device output and by this electric signal output to computer, the photooptical data of measurement is by computer disposal analysis and evaluation
Led quality of welding spot.
Encapsulation led quality of welding spot detection method, comprises the following steps:
(1) build quality of welding spot detection means, led lamp beads to be measured are fixed on specimen holder, try one's best in fixing lamp bead
Ensure that lamp bead is aligned with photodetector, to obtain maximum output light intensity;
(2) the firing current value of current source is set, enables led lamp beads normal work in circuit;
(3) in order to obtain complete transient response, computer elder generation control data capture card is started working, then control electric current source
Open, computer reads the time dependent data of capture card light intensity and the time dependent data of circuital current at a high speed simultaneously,
And preserved;
(4) by computer, light intensity and the time dependent transient data of electric current are processed, obtain circuital current and light
The fall time of strong transient response curve and magnitude parameters.Fall time is electric current or light intensity from maximum to stablizing amplitude
Time difference, amplitude is electric current or amplitude during stabilized intensity;
(5) by the fall time of tested led lamp beads with stablize magnitude parameters and be compared with default threshold value, you can realization
The evaluation of lamp bead quality of welding spot.If the solder joint of tested lamp bead is defective, the fall time of the response curve of electric current and light intensity
Longer, amplitude is less.
The measuring principle of the present invention:
Led chip is in the nature pn-junction diode, can be equivalent to junction capacity c, bulk resistor rjWith series resistance rsThe electricity of composition
Road, as shown in Figure 3.Failure welding, the defect such as soldered ball is excessive, solder joint Microfocus X-ray tube can lead to solder joint resistance to increase, and due to welding
The presence of layer intermetallic compound, defect solder joint is introduced into parasitic capacitance and inductance, and equivalent circuit is as shown in Figure 4.Defect solder joint
Introduce contact resistance and parasitic capacitance by affect led open transient current and light intensity curve, thus measurement led open transient state
Electric current and light intensity curve, it is possible to achieve the detection to led welding quality.
As shown in figure 3, loading step voltage u (t) to circuit, amplitude is u to the equivalent circuit of led chip, if flowing through resistance
rjElectric current be i1(t), the transient response of counting circuit:
Abbreviation obtains differential equation of first order:
When t < when 0, i1(0+)=i1(0-)=0;i2(0+)=i2(0-)=0
As t > 0 when,
Solve:
Total current is:
When there is weld defect, defect solder joint will introduce contact resistance (r on the equivalent circuit of led chipp) and post
Raw inductance (lp), electric capacity (cp) parasitic circuit that forms, as shown in figure 4, set flowing through resistance rjAnd rpElectric current be respectively i2(t)、
i3(t), circuit total current is i, the transient effect of counting circuit:
Arrange:
When t < when 0,
As t > 0 when,
Now the total current of equivalent circuit is:
Make i1(t)=x, i2(t)=y, i2' (t)=z carries out depression of order to differential equation of higher order (6), (7), obtains differential side
Journey group:
Solve the circuit transient response result obtaining under two kinds of different situations as shown in Figure 5:
Step voltage is loaded to circuit, the voltage due to electric capacity two ends is unable to transition, and when initial, voltage is all loaded into electricity
Resistance rs, therefore current over pulse in two ends.Electric capacity gradually charges, and resistance both end voltage reduces, and circuit total current is gradually reduced, electricity
Capacity charge finishes rear resistance both end voltage and keeps stable, and now circuit total current keeps constant, as shown in Figure 5.Normal lamp bead and
Defect welds lamp bead, and under the step signal of identical voltage encourages, the transient current obtaining responds in amplitude and fall time
All variant, weld defect leads to contact resistance to increase, introduces parasitic capacitance inductance, leads to stabling current less than normal, i2<i1, decline
Time is longer, t2>t1.Electric current thus according to switching transient and Intensity response curve, obtain fall time and stablize amplitude, with
Default threshold value is compared, you can differentiate led Product jointing quality, realizes quality of welding spot detection.
Due to employing technique scheme, the present invention has the advantage that:
The present invention, according to the electric current of led switching transient and Intensity response curve, obtains fall time and stablizes amplitude, and pre-
If threshold value be compared, you can immediately differentiate led Product jointing quality, realize butt welding point Quality estimation.Due to not needing corruption
The step of erosion encapsulated layer, test process is very quick, is especially advantageous for the welding procedure of encapsulating products is tested and analyzed.
Brief description
In order that the object, technical solutions and advantages of the present invention are clearer, below in conjunction with accompanying drawing the present invention is made into
The detailed description of one step, wherein:
Fig. 1 is quality of welding spot structure of the detecting device figure;
Fig. 2 is quality of welding spot structure of the detecting device figure in embodiment;
Fig. 3 is standard led equivalent circuit diagram;
Fig. 4 is failure welding led equivalent circuit diagram;
Fig. 5 is current transient response diagram;
Fig. 6 is normalization transient current change curve;
Fig. 7 is matching transient current change curve.
Specific embodiment
Below with reference to accompanying drawing, the preferred embodiments of the present invention are described in detail;It should be appreciated that preferred embodiment
Only for the present invention is described, rather than in order to limit the scope of the invention.
As shown in figure 1, encapsulation led quality of welding spot detection means, including current source, specimen holder, current measuring unit, photoelectricity
Detector, data collecting card and computer;Led work on described driven with current sources specimen holder, the electric current of led switching moments by
Current measuring unit obtains, and exports to computer;Described photodetector is arranged on the dead ahead of specimen holder, for gathering
This optical signal is simultaneously converted to the signal of telecommunication by optical signal that led sends;The outfan of described photodetector is with data collecting card even
Connect, data collecting card is connected with computer, described data collecting card obtains the signal of telecommunication of photodetector output and by this telecommunications
Number export to computer, the photooptical data of measurement is by computer disposal analysis and evaluation led quality of welding spot.In the present embodiment, electricity
Flow metering unit includes measuring resistance and the voltage probe connected with led, and the resistance of known resistance is gone here and there with tested lamp bead
Connection, realizes the measurement to led transient current, and voltage probe is connected on the transient changing feelings that resistance two ends obtain resistance both end voltage
Condition, the voltage measured by voltage probe is divided by the transient current change of the resistance as circuit of resistance.
In the present embodiment, tested led lamp beads are high power white light led lamp beads, and its power is 1w, and rated operational current is
350ma, measuring samples come from 5 lamp bead of same batch of same model.Encapsulation led quality of welding spot detection method, including with
Lower step:
(1) build quality of welding spot detection means as shown in Figure 2, tested led lamp beads are fixed on specimen holder;
(2) the firing current value of setting current source is the rated operational current 350ma of lamp bead;
(3) computer elder generation control data capture card is started working, then control electric current source is opened, and computer reads at a high speed simultaneously
The time dependent data of capture card light intensity and the time dependent data of circuital current, and preserved;
(4) by computer, light intensity and the time dependent transient data of electric current are processed, obtain circuital current and light
Fall time of strong transient response curve and stablize magnitude parameters.Fall time is for electric current or light intensity from maximum to stabilizing panel
Time difference between value, amplitude is amplitude when electric current or stabilized intensity, and the normallized current of led changes over curve such as Fig. 6
Shown;
(5) by the fall time of tested led lamp beads with stablize magnitude parameters and be compared with default threshold value, you can realization
The evaluation of lamp bead quality of welding spot.
Because instrument has measurement error, there is certain ripple in the therefore actual circuital current transient response curve obtaining
Dynamic, in data handling, data is carried out boltzmann curve matching, as shown in fig. 7, thus accurate electricity can be obtained
The fall time of road current transient response and magnitude parameters.
Fig. 7 is matching transient current change curve, and fitting formula is:
In formula, a1、a2、x0, b be parameter.In formula, b is less, and curve is steeper, declines faster, represents and reaches surely from maximum
The temporal characteristics amount of definite value;y|x→+∞=a2, the stable amplitude of curve is mainly by parameter a2Determine.
In the present embodiment, threshold value is to be set by the following method:
The a collection of lamp bead of measured in advance same model, obtains the fall time of lamp bead and stablizes magnitude parameters, be satisfied by normal state
Distribution, average is respectively μb=24.62, μa2=0.97556, standard deviation sigmab=2.31, σa2=0.001743.Defect solder joint introduces
Contact resistance and parasitic capacitance can lead to led's to hold that transient current and light intensity curve fall time are elongated, stablize amplitude
Reduce, choose fall time and stablize magnitude parameters threshold value for μ+3 σ, i.e. b=31.55, a2=0.97033.Fall time gets over
Greatly, stablize amplitude less, then lamp bead quality of welding spot is poorer, the threshold range that therefore welding point defect lamp bead is rejected is set as b ∈
(31.55 ,+∞), a2∈ (0,0.97033), by entering in the led lamp beads rejecting threshold range with stablizing amplitude to fall time
The destructive detection of row, finds there are obvious Welding Problems.
The transient current change curve of five sample lamp bead is carried out curve fitting, obtains fall time, stablize amplitude ginseng
Number b and a2Numerical value as shown in the table:
Table 1 matched curve b and a2Value contrast
|
led1 |
led2 |
led3 |
led4 |
led5 |
b |
20.96 |
26.10 |
26.26 |
25.29 |
67.57 |
a2 |
0.97722 |
0.97537 |
0.97519 |
0.97451 |
0.94908 |
Tested lamp bead the Fitting Calculation obtains fall time parameter b and stablizes magnitude parameters a2Numerical value as shown in table 1 it is known that
The fall time parameter of led5 is all rejecting threshold range with stablizing magnitude parameters, therefore there is quality of welding spot problem, further
Analysis understands that the fall time of lamp bead led5 compares other lamp bead greatly, amplitude when stablizing is little compared with other lamp bead, then led5 solder joint
Contact resistance is larger, shows failure welding, and the parasitic capacitance of introducing, inductance are larger, then there is microvoid shape between solder joint and pad
Become capacity plate antenna effect, thus speculate that led5 problems of welded quality that may be present is rosin joint.
The present invention, according to the electric current of led switching transient and Intensity response curve, obtains fall time and stablizes amplitude, and pre-
If level threshold value be compared, you can differentiate led Product jointing quality, realize butt welding point mass Non-Destructive Testing.
The foregoing is only the preferred embodiments of the present invention, be not limited to the present invention it is clear that those skilled in the art
Member the present invention can be carried out various change and modification without departing from the spirit and scope of the present invention.So, if the present invention
These modifications and modification belong within the scope of the claims in the present invention and its equivalent technologies, then the present invention is also intended to comprise these
Including change and modification.