CN108317979B - Method for measuring coplanarity of solder balls of BGA (ball grid array) packaged chip - Google Patents
Method for measuring coplanarity of solder balls of BGA (ball grid array) packaged chip Download PDFInfo
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- CN108317979B CN108317979B CN201711304348.XA CN201711304348A CN108317979B CN 108317979 B CN108317979 B CN 108317979B CN 201711304348 A CN201711304348 A CN 201711304348A CN 108317979 B CN108317979 B CN 108317979B
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B15/00—Measuring arrangements characterised by the use of electromagnetic waves or particle radiation, e.g. by the use of microwaves, X-rays, gamma rays or electrons
Abstract
The invention discloses a method for measuring the coplanarity of solder balls of a BGA (ball grid array) packaged chip. According to the method, a gamma photon source provided with a collimator is used for radiating the BGA packaging chip in a safe environment, and gamma photons are reflected to a receiving processor after acting with the chip. The scintillator in the receiving processor receives the photons which are back-scattered by the chip, the photon counting frequency is obtained by the processing circuit after the photons are multiplied by the photomultiplier, and the height from the top surface of the solder ball to the receiving processor is obtained through simulation, so that the height of the solder ball is obtained.
Description
Technical Field
the invention relates to the field of measurement, in particular to a method for measuring the coplanarity of solder balls of a BGA (ball grid array) packaged chip.
Background
The pin coplanarity is one of the most important indexes for detecting whether the device is qualified or not. Although the solder balls and the solder paste are remelted to form solder joints to realize the connection between the chip and the chip substrate during surface mounting, thereby overcoming the coplanarity problem caused by solder balls with different heights, if the coplanarity of the solder ball pins of the device exceeds standard, the contact between individual solder balls and the board is poor during mounting, which can cause missing connection and virtual connection.
after the packaged device is mounted on the board, the pin welding points are hidden at the bottom of the chip, so that the quality of the welding points is difficult to detect in a direct observation mode, and the surface is difficult to repair when the surface is assembled. Therefore, before surface mounting, the coplanarity of the leads needs to be detected. At present, the common methods for performing nondestructive testing on the height of a solder ball of a pin solder joint include: manual visual inspection, radiation inspection, and automated optical inspection.
the gamma photon height measurement technology can realize dynamic measurement of low height, and the precision meets the requirement. In addition, because the simulation analysis based on the interaction technology of gamma photons and substances is very mature, a Monte Carlo method can be used for establishing a model and carrying out simulation analysis. However, this measurement method is not applied to the field of measurement of coplanarity of solder balls.
Disclosure of Invention
Aiming at the defects of the prior art, the invention aims to solve the technical problem of providing a method for measuring the coplanarity of solder balls of a BGA package chip.
The technical scheme for solving the technical problem is to provide a method for measuring the coplanarity of the solder balls of the BGA packaged chip, which is characterized by comprising the following steps of:
(1) Building a measuring device: the distance between the gamma photon source and the receiving processor is larger than the size of the chip, the receiving processor can receive photons which are backscattered by the gamma photon source, and the gamma photon source and the receiving processor are positioned at the same height; the angle of a collimator of the gamma photon source is controllable;
(2) the gamma photon source emits photons to the solder balls and the surface of the chip substrate through the collimator, and supposing that the tested chip has m multiplied by n solder balls, the sequence i of each row of solder balls is 1, 2 and 3 … … m, and the sequence j of each column of solder balls is 1, 2 and 3 … … n, so that the height from the top surface of each solder ball to the receiving processor is h1ij(ii) a The height from the surface of the chip substrate to the receiving processor is h2(ii) a The number of photons back scattered by the photons on the surface of the chip substrate to the receiving processor should be a constant, and then h corresponds to the number of photons2Is also a constant; then, to obtain a certain solder ball height hijIt is only necessary to obtain the height h from the top surface of the solder ball to the receiving processor1ijthen the method is finished;
hij＝h2-h1ij,(i＝1,2,3......m,j＝1,2,3......n) (1)
The number of photons back scattered from the top surface of the solder ball to the receiving processor is NijConverted into the corresponding photon counting frequency f (h)1ij) I.e. by
f(h1ij)＝Nij×A(E,h1ij),(i＝1,2,3......m,j＝1,2,3......n) (2)
wherein, A (E, h)1ij) For photons incident at different distancesthe conversion coefficient of the electronic equipment after the scintillator is known by a processing circuit;
Number of photons N that are backscattered back to the receiving processor at the top surface of the solder ballijBy photon fluxAnd scintillator effective area SEcan be obtained by
Nij＝φij×SE,(i＝1,2,3......m,j＝1,2,3......n) (3)
In the formula (I), the compound is shown in the specification,determined by the light source parameters and the relative position of the hardware in the device;
Simulating the position relation between the hardware of the current device and the angle of the collimator by adopting MCNP software to obtain a curve between the photon counting frequency and the height, and then obtaining the photon counting frequency f (h) of a certain current solder ball according to the above1ij) The height h from the top surface of the solder ball to the receiving processor is obtained1ijFurther obtain the height h of the solder ballij；
(3) Adjusting the angle of the collimator, and repeating the step (2) to obtain the height h of each solder ball of m multiplied by n solder balls of the tested chipijAnd further obtain coplanarity information.
Compared with the prior art, the invention has the beneficial effects that:
1. The gamma photon measurement technology is used in the field of BGA solder ball coplanarity measurement, the gamma photon measurement technology is used in the aspect of measuring height distance, the method is innovatively used for measuring height difference, the gamma photon dynamic measurement precision is high, and the obtained result is more accurate and reliable;
2. The solder ball cannot be touched in the measuring process, so that the failure of the solder ball caused by measurement cannot be caused;
3. The sensitivity of gamma photons is high, and the measurement by utilizing the gamma photon technology is quick and effective;
4. The gamma photon has good anti-interference performance after long-term use, simple operation and easy subsequent development.
drawings
FIG. 1 is a schematic diagram illustrating the operation of one embodiment of the method for measuring the coplanarity of solder balls of a BGA package chip according to the present invention;
Detailed Description
Specific examples of the present invention are given below. The specific examples are only intended to illustrate the invention in further detail and do not limit the scope of protection of the claims of the present application.
The invention provides a method for measuring the coplanarity of solder balls of a BGA packaged chip. According to the method, a gamma photon source 1 with a collimator is used for radiating the BGA encapsulation chip in a safe environment, and gamma photons are reflected to a receiving processor 2 after acting with the chip. The scintillator in the receiving processor 2 receives the photons which are back-scattered by the chip, the photon counting frequency is obtained by the processing circuit after the photons are multiplied by the photomultiplier, the height from the top surface of the solder ball to the receiving processor is obtained through simulation, and then the height of the solder ball is obtained.
The method for measuring the coplanarity of the solder balls of the BGA packaging chip, which is designed by the invention, is based on the following hardware design, as shown in figure 1: the hardware comprises a gamma photon source 1 and a receiving processor 2; a collimator is arranged in the gamma photon source 1; the receiving processor 2 is internally provided with a scintillator, a photomultiplier and a processing circuit.
The invention provides a method for measuring the coplanarity of solder balls of a BGA (ball grid array) packaged chip (short for method), which is characterized by comprising the following steps:
(1) Building a measuring device: the distance between the gamma photon source 1 and the receiving processor 2 is larger than the size of a chip, the receiving processor 2 can receive photons which are backscattered by the gamma photon source 1, and the gamma photon source 1 and the receiving processor 2 are positioned at the same height; the gamma-ray source 1 is an isotropic point source137Cs with the activity of 298mCi and the energy of 0.662MeV and controllable collimator angle;
(2) The gamma photon source 1 emits photons to the solder balls and the surface of the chip substrate through the collimator, and assuming that the tested chip has m × n solder balls, the sequence i of each row of solder balls is 1, 2, 3 … … m, and the sequence j of each column of solder balls is 1, 2, 3 … … n, so that the height from the top surface of each solder ball to the receiving processor 2 is h1ij(ii) a The height h from the surface of the chip substrate to the receiving processor 22(ii) a The number of photons back scattered by the photons on the surface of the chip substrate to the receiving processor 2 should be a constant, so that the number of photons corresponds to h2is also a constant; then, to obtain a certain solder ball height hijIt is only necessary to obtain the height h from the top surface of the solder ball to the receiving processor 21ijThen the method is finished;
hij＝h2-h1ij,(i＝1,2,3......m,j＝1,2,3......n) (1)
The number of photons back scattered at the top surface of the solder ball to the receiving processor 2 is NijConverted into the corresponding photon counting frequency f (h)1ij) I.e. by
f(h1ij)＝Nij×A(E,h1ij),(i＝1,2,3......m,j＝1,2,3......n) (2)
Wherein, A (E, h)1ij) The conversion coefficient of the electronic equipment after the photons are incident on the scintillator under different distances can be known according to the processing circuit;
The number of photons N that are backscattered at the top surface of the ball back to the receiving processor 2ijBy photon fluxAnd scintillator effective area SEcan be obtained by
Nij＝φij×SE,(i＝1,2,3......m,j＝1,2,3......n) (3)
In the formula (I), the compound is shown in the specification,Determined by the light source parameters and the relative position of the hardware in the device;
Simulating the position relation between the hardware of the current device and the angle of the collimator by adopting MCNP software to obtain a curve between the photon counting frequency and the height, and then obtaining the photon counting frequency f (h) of a certain current solder ball according to the above1ij) The height h from the top surface of the solder ball to the receiving processor 2 is obtained1ijFurther obtain the height h of the solder ballij；
(3) Adjusting the angle of the collimator, and repeating the step (2) to obtain the height h of each solder ball of m multiplied by n solder balls of the tested chipijAnd further obtain coplanarity information.
nothing in this specification is said to apply to the prior art.
Claims (2)
1. A method for measuring the coplanarity of solder balls of a BGA packaged chip is characterized by comprising the following steps:
(1) Building a measuring device: the distance between the gamma photon source and the receiving processor is larger than the size of the chip, the receiving processor can receive photons which are backscattered by the gamma photon source, and the gamma photon source and the receiving processor are positioned at the same height; the angle of a collimator of the gamma photon source is controllable;
(2) The gamma photon source emits photons to the solder balls and the surface of the chip substrate through the collimator, and supposing that the tested chip has m multiplied by n solder balls, the sequence i of each row of solder balls is 1, 2 and 3 … … m, and the sequence j of each column of solder balls is 1, 2 and 3 … … n, so that the height from the top surface of each solder ball to the receiving processor is h1ij(ii) a The height from the surface of the chip substrate to the receiving processor is h2(ii) a The number of photons back scattered by the photons on the surface of the chip substrate to the receiving processor should be a constant, and then h corresponds to the number of photons2Is also a constant; then, to obtain a certain solder ball height hijit is only necessary to obtain the height h from the top surface of the solder ball to the receiving processor1ijThen the method is finished;
hij＝h2-h1ij,(i＝1,2,3......m,j＝1,2,3......n) (1)
The number of photons back scattered from the top surface of the solder ball to the receiving processor is NijConverted into the corresponding photon counting frequency f (h)1ij) I.e. by
f(h1ij)＝Nij×A(E,h1ij),(i＝1,2,3......m,j＝1,2,3......n) (2)
Wherein, A (E, h)1ij) The conversion coefficient of the electronic equipment after the photons are incident on the scintillator under different distances can be known according to the processing circuit;
Photons are backscattered at the top surface of the solder ball and returned to the receiving processPhoton number N of the deviceijBy photon fluxAnd scintillator effective area SEcan be obtained by
Nij＝φij×SE,(i＝1,2,3......m,j＝1,2,3......n) (3)
In the formula (I), the compound is shown in the specification,Determined by the light source parameters and the relative position of the hardware in the device;
Simulating the position relation between the hardware of the current device and the angle of the collimator by adopting MCNP software to obtain a curve between the photon counting frequency and the height, and then obtaining the photon counting frequency f (h) of a certain current solder ball according to the above1ij) The height h from the top surface of the solder ball to the receiving processor is obtained1ijFurther obtain the height h of the solder ballij；
(3) adjusting the angle of the collimator, and repeating the step (2) to obtain the height h of each solder ball of m multiplied by n solder balls of the tested chipijAnd further obtain coplanarity information.
2. The method of claim 1, wherein the gamma photon source is an isotropic point source137Cs, activity 298mCi, energy 0.662 MeV.
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| CN113052797B (en) * | 2021-03-08 | 2024-01-05 | 江苏师范大学 | BGA solder ball three-dimensional detection method based on depth image processing |
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| JPH1123234A (en) * | 1997-06-30 | 1999-01-29 | Just:Kk | Method and instrument for measuring height of solder ball of bga |
| CN1847784A (en) * | 2005-04-05 | 2006-10-18 | 华为技术有限公司 | Device pin coplanarity measuring method |
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| CN201844818U (en) * | 2010-11-18 | 2011-05-25 | 华中科技大学 | BGA (ball grid array) coplanarity measurement system based on projection Moire principle |
| CN103308007A (en) * | 2013-05-24 | 2013-09-18 | 华南理工大学 | System and method for measuring coplanarity of integrated circuit (IC) pins through multistage reflection and raster imaging |
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| JPH1123234A (en) * | 1997-06-30 | 1999-01-29 | Just:Kk | Method and instrument for measuring height of solder ball of bga |
| CN1847784A (en) * | 2005-04-05 | 2006-10-18 | 华为技术有限公司 | Device pin coplanarity measuring method |
| CN101454637A (en) * | 2006-05-23 | 2009-06-10 | 新加坡科技研究局 | Method and apparatus for bump inspection |
| CN201844818U (en) * | 2010-11-18 | 2011-05-25 | 华中科技大学 | BGA (ball grid array) coplanarity measurement system based on projection Moire principle |
| CN103308007A (en) * | 2013-05-24 | 2013-09-18 | 华南理工大学 | System and method for measuring coplanarity of integrated circuit (IC) pins through multistage reflection and raster imaging |
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