CN103954629B - Quality detection device and method of encapsulation LED solder joint - Google Patents

Abstract

The invention discloses a quality detection device and method of an encapsulation LED solder joint. The device comprises a current source, a sample holder, a current detection unit, a photoelectric detector, a data acquisition card and a computer; the current source drives the LED on the sample holder to work; the current detection unit obtains instantaneous current occurring by switching the LED and outputs the instantaneous current to the computer; the photoelectric detector is arranged in front of the sample holder to collect an optical signal sent by the LED and converts the optical signal into an electrical signal; the output end of the photoelectric detector is connected with the data acquisition card; the data acquisition card is connected with the computer; the data acquisition card obtains the electrical signal output by the photoelectric detector and outputs the electrical signal to the computer; and the computer processes and analyzes the measured photoelectrical data to evaluate the quality of the LED solder joint. The invention utilizes a new quality detection method of an encapsulation LED solder joint; and according to the instantaneous current occurring by switching the LED and response curve of light intensity, fall time and stable amplitude are obtained to be compared with preset thresholds, namely the soldering quality of an LED product can be identified so as to realize nondestructive testing of the quality of the solder joint.

Description

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 r_jWith series resistance r_sThe 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 r_jElectric current be i₁(t), the transient response of counting circuit:

$r_{j}i\left(t\right)+r_s[i_1\left(t\right)+r_j{c}_j\frac{{\mathrm{di}}_1\left(t\right)}{\mathrm{dt}}]=u\left(t\right)---\left(1\right)$

Abbreviation obtains differential equation of first order:

$r_j{c}_j\frac{{\mathrm{di}}_1\left(t\right)}{\mathrm{dt}}+(r_j+r_s)i_1\left(t\right)=u\left(t\right)---\left(2\right)$

When t < when 0, i₁(0+)=i₁(0-)=0；i₂(0+)=i₂(0-)=0

As t > 0 when, $r_j{c}_j\frac{{\mathrm{di}}_1\left(t\right)}{\mathrm{dt}}+(r_j+r_s)i_1\left(t\right)=u$

Solve:

$i_1\left(t\right)=\frac{u}{r_s+r_j}(1-e^{-\frac{r_s+r_j}{r_j{c}_j}t})---\left(3\right)$

Total current is: $i\left(t\right)=i_1\left(t\right)+i_{\mathrm{cj}}\left(t\right)=i_1\left(t\right)+r_j{c}_j\frac{{\mathrm{di}}_1\left(t\right)}{\mathrm{dt}}=u{e}^{-\frac{r_s+r_j}{r_j{c}_j}t}$

When there is weld defect, defect solder joint will introduce contact resistance (r on the equivalent circuit of led chip_p) and post Raw inductance (l_p), electric capacity (c_p) parasitic circuit that forms, as shown in figure 4, set flowing through resistance r_jAnd r_pElectric current be respectively i₂(t)、 i₃(t), circuit total current is i, the transient effect of counting circuit:

$\begin{array}{c}i=i_2\left(t\right)+r_j{c}_j\frac{{\mathrm{di}}_2\left(t\right)}{\mathrm{dt}}\\ =i_3\left(t\right)+c_p\frac{d[l_p\frac{{\mathrm{di}}_3\left(t\right)}{\mathrm{dt}}+i_3\left(t\right)r_p]}{\mathrm{dt}}\\ =i_3\left(t\right)+c_p{l}_p\frac{d^2{i}_3\left(t\right)}{{\mathrm{dt}}^2}+r_p{c}_p\frac{{\mathrm{di}}_3\left(t\right)}{\mathrm{dt}}\end{array}---\left(5\right)$

Arrange: $i_2\left(t\right)+r_j{c}_j\frac{{\mathrm{di}}_2\left(t\right)}{\mathrm{dt}}=i_3\left(t\right)+c_p{l}_p\frac{d^2{i}_3\left(t\right)}{{\mathrm{dt}}^2}+r_p{c}_p\frac{{\mathrm{di}}_3\left(t\right)}{\mathrm{dt}}---\left(6\right)$

When t < when 0, $i_2(0+)=i_2(0-)=0;i_3(0+)=i_3(0-)=0;\frac{{\mathrm{di}}_3\left(t\right)}{\mathrm{dt}}{|}_{t=0}=0$

As t > 0 when, $u=r_j{i}_2\left(t\right)+r_s[i_2\left(t\right)+r_j{c}_j\frac{{\mathrm{di}}_2\left(t\right)}{\mathrm{dt}}]+l_p\frac{{\mathrm{di}}_3\left(t\right)}{\mathrm{dt}}+i_3\left(t\right)r_{p1}---\left(7\right)$

Now the total current of equivalent circuit is:

$i=i_2\left(t\right)+r_j{c}_j\frac{{\mathrm{di}}_2\left(t\right)}{\mathrm{dt}}---\left(8\right)$

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:

$\left\{\begin{array}{c}{x}^{\&prime;}=-\frac{1}{r_j{r}_s{c}_j}[(r_j+r_s)x+r_{p}y+r_{p}z+u]\\ y^{\&prime;}=z\\ z^{\&prime;}=-\frac{1}{r_s{c}_p{l}_p}[r_{j}x+(r_p+r_s)y+(l_p+r_s{r}_p{c}_p)z+u]\end{array}\right.$

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 r_s, 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:

$y=\frac{(a_1-a_2)}{1+e^{(x-x_0)/b}}+a_2$

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 μ_b=24.62, μ_a2=0.97556, standard deviation sigma_b=2.31, σ_a2=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.

Claims (2)

1. encapsulation led quality of welding spot detection means it is characterised in that: include 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 is obtained by current measuring unit, and defeated Go out to computer；

Described photodetector is arranged on the dead ahead of specimen holder, for gathering the optical signal that led sends and turning this optical signal It is changed to the signal of telecommunication；

The outfan of described photodetector is connected with data collecting card, and data collecting card is connected with computer, data collecting card The collection time dependent data of light intensity, current measuring unit obtains the time dependent data of circuital current；Computer is to light The strong and time dependent transient data of electric current is processed, during the decline of transient response curve of acquisition circuital current and light intensity Between and magnitude parameters；Described data collecting card obtains the signal of telecommunication of photodetector output and by this electric signal output to calculating Machine, the photooptical data of measurement is by computer disposal analysis and evaluation led quality of welding spot.

2. usage right require the method that detected of led quality of welding spot detection means described in 1 it is characterised in that: include following Step:

(1) build quality of welding spot detection means, led lamp beads to be measured are fixed on specimen holder；

(2) the firing current value of current source is set, enables led lamp beads normal work in circuit；

(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 data simultaneously The time dependent data of light intensity of capture card collection 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 intensity The fall time of transient response curve and magnitude parameters；Fall time be electric current or light intensity from maximum to stablize amplitude when Between poor, 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 realize lamp bead The evaluation of quality of welding spot.