Method for estimating coplanarity of ball grid array packaging circuit before ball mounting

Abstract

The invention discloses a method for estimating coplanarity of a ball grid array packaging circuit before ball mounting, which comprises the following steps of: measuring coordinates of a specific position point of a ball mounting surface: measuring vertical coordinates of the specific position point of the ball mounting surface of the packaging circuit, including a central point, a vertex and a midpoint of a connecting line of the vertex and the central point; key point coordinates are determined, specifically, the height of each point is obtained according to the height difference between each vertex, the height difference between the midpoint and the central point, the midpoint with the largest height difference between the midpoint and the nearest vertex is selected as an extreme point, the nearest vertex is a high-weight vertex, and two vertexes adjacent to the vertex are low-weight vertexes; determining a reference plane: determining the reference plane by the high-weight vertex and the two low-weight vertexes; simplified calculation of the projection height of the extreme point: calculating the height of the projection point of the extreme point on the reference plane by adopting a simplified formula; and coplanarity estimation: the height difference between the extreme point and the projection point thereof is a coplanarity estimation value. The coplanarity estimation method provided by the invention can effectively estimate the coplanarity of each process before ball mounting.

Description

Technical Field

[0001] The invention belongs to the technical field of hybrid integrated circuit production and manufacturing, in particular to a method for estimating the coplanarity of a ball grid array packaging circuit before ball planting. Background Art

[0002] Ball Grid Array (BGA) packaging is an array made at the bottom of the package substrate, and the solder balls are used as the I / O terminals of the circuit to interconnect with the printed circuit board (PCB). The device packaged using this technology is a surface mount device. Ball grid array is a surface mount package for multi-pin LSI, in which spherical contacts are made in an array on the back of the substrate as pins and LSI is assembled on the front of the substrate (some BGA chips and lead terminals are on the same side of the substrate).

[0003] Although the organic substrate has a low coefficient of thermal expansion, the thermal mismatch between different devices becomes more and more obvious as the package size increases. With the improvement of wafer processing technology capabilities, the size of single-core bare chips is getting larger and larger, which increases the thermal stress between the bare chip and the organic substrate after welding. Due to the flip-chip packaging form, in order to protect the reliability of the bare chip bumps, the bare chip needs to be bottom-filled after welding. This operation not only protects the bare chip bumps from stress release damage, but also reduces a means of stress release during thermal deformation. The larger the package size and the higher the integration density of the hybrid integrated circuit, the more complex the warpage changes during the packaging process, and the more difficult the package coplanarity optimization analysis is. The weldability of the integrated circuit puts forward requirements on the coplanarity of the solder balls. If the coplanarity exceeds the weldable range, even the most advanced integrated circuits cannot be applied in engineering.

[0004] Before balling the BGA circuit, the processes of flip-chip core mounting, cap attachment, post-cap attachment baking, and SAT dehumidification after cap attachment will all affect the final coplanarity, so it is particularly important to measure or estimate the coplanarity of the BGA package circuit after each process before balling. Obtaining the coplanarity results after each process can, on the one hand, locate the degree of influence of each process on the coplanarity, and on the other hand, provide a basis for judging the effectiveness of the process improvement measures. The system-level package circuit integrates bare chips such as FPGA, DSP, DDR, and ADC, which are of high value. Obtaining the coplanarity value in advance during the processing and formulating corresponding emergency corrective measures can avoid batch coplanarity deviation after the packaging is completed, thereby avoiding great cost losses and more batch processing cycles. Due to the lack of coplanarity measurement methods in the process, the packaging factory cannot effectively implement too many process improvement measures. Obtaining the coplanarity value in advance during the processing can accurately locate the process that has a greater impact on the coplanarity, and can evaluate the effectiveness of the process improvement measures, which can accelerate the process of packaging process improvement and development of the packaging factory and promote the process improvement and development of the integrated circuit packaging industry.

[0005] However, the coplanarity measuring instruments currently on the market are all based on the principle of optical detection, automatically identifying the pin distribution of the device, measuring the pin height difference, and then using the general coplanarity algorithm to solve the coplanarity value. This method can be used to measure the coplanarity data after the BGA package circuit is finally implanted, but it cannot be used to measure the coplanarity of the semi-finished BGA package circuit before implanting. According to the existing data, no other method has been found to estimate the coplanarity of the BGA package circuit before implanting.

[0006] Therefore, the problem in the prior art is that there is a lack of effective methods for measuring or estimating the coplanarity of BGA packaged circuits before ball implantation. Summary of the invention

[0007] The purpose of the present invention is to provide a method for estimating the coplanarity of a ball grid array package circuit before ball implantation, which can effectively estimate the coplanarity of each process before ball implantation and facilitate the control and evaluation of the influence of each link before ball implantation on the circuit coplanarity.

[0008] The technical solution to achieve the purpose of the present invention is:

[0009] A method for estimating the coplanarity of a ball grid array package circuit before ball implantation comprises the following steps:

[0010] Coordinate measurement of specific position points on the ball planting surface: measuring the vertical coordinates of 9 specific position points on the ball planting surface of the package circuit; the 9 specific positions are respectively the center point of the package circuit, the 4 vertices of the package circuit, and the midpoint of the lines connecting the 4 vertices of the package circuit and the center point of the package circuit;

[0011] Determine the coordinates of key points: According to the height difference between each package circuit vertex and midpoint and the center point of the package circuit, obtain the height of each package circuit vertex and midpoint, select the midpoint with the largest height difference with the nearest package circuit vertex as the extreme point, the package circuit vertex closest to the extreme point as the high-weight vertex, and the two package circuit vertices adjacent to the high-weight vertex as low-weight vertices;

[0012] Determine the reference plane: a plane is jointly determined by the high-weight vertex and the two low-weight vertices, and the plane is the reference plane;

[0013] Simplified calculation of the projection height of the extreme point: using a simplified formula to calculate the height of the projection point of the extreme point on the reference plane;

[0014] Coplanarity estimation: The coplanarity estimation value is calculated based on the height of the extreme point and the height of the projection point of the extreme point on the reference plane.

[0015] Preferably, the extreme point determination step comprises:

[0016] Calculate the height of the non-center point: According to the four vertices P1, P2, P3, and P4 of the package circuit, and the four midpoints P of the lines connecting the four vertices of the package circuit and the center point of the package circuit 1’ , P 2’ , P 3’ , P 4’ The vertical coordinate of the package circuit center point is calculated to obtain the height of each non-center point, that is, each vertex and midpoint relative to the package circuit center point.

[0017] The non-center point height is calculated according to the following formula:

[0018] H Pi =V Pi -V P0

[0019] Among them, H Pi is the height of the non-central point Pi, V Pi is the vertical coordinate measurement value of the non-center point Pi, i = 1, 2, 3, 4, 1', 2', 3', 4', V P0 It is the vertical coordinate measurement value of the center point of the package circuit;

[0020] Determination of extreme value points: The warpage value of each vertex of the package circuit is obtained by subtracting the height of the midpoint closest to the vertex from the height of each vertex of the package circuit, and the midpoint closest to the vertex with the largest warpage value is selected as the extreme value point;

[0021] Determine high-weight vertices: select the vertex closest to the extreme point as a high-weight vertex, and the height value of the high-weight vertex is used as the high-weight value;

[0022] Determine low-weight vertices: select two vertices adjacent to the high-weight vertex as low-weight vertices, and use the height values ​​of the low-weight vertices as low-weight values.

[0023] Preferably, the step of simplifying the calculation of the extreme point projection height is specifically as follows:

[0024] The approximate height of the projection point of the extreme point on the reference plane is calculated according to the following simplified formula:

[0025] H S =(H H ×2+H L1 +H L2 )

[0026] Among them, H S is the simplified projection point height, H H is a high weight value, H L1 and H L2 are two low weight values.

[0027] Preferably, the coplanarity estimation step is specifically as follows:

[0028] The estimated coplanarity value is calculated as follows:

[0029] C=H Pi′ =-H S

[0030] Where C is the coplanarity, H is Pi′ is the height of the extreme point, H S is the projection point height.

[0031] Compared with the prior art, the present invention has the following significant advantages:

[0032] 1. Effective estimation of coplanarity: Based on a simplified algorithm model and simple measurement, the present invention realizes a method for estimating the coplanarity of BGA packaged circuits before ball implantation, provides an effective means for evaluating the coplanarity of circuits before ball implantation, and fills the gap in evaluation methods during the current window period of industrial equipment development.

[0033] 2. Facilitate early assessment of process impact: The present invention estimates the coplanarity data based on the measured data of each state, which can effectively support the impact of each process on the degree of coplanarity change, and can be used to provide a basis for judging the impact of each link of the packaging process on the circuit coplanarity. However, the existing technology only measures the final coplanarity result after the BGA packaging circuit is implanted, and cannot accurately locate the process with greater impact, and can only rely on simulation data. In most current packaging processes, it is still impossible to accurately establish the environmental conditions of each packaging process and simulate and derive guiding simulation data.

[0034] The present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 It is the main flow chart of the method for estimating the coplanarity of a BGA package circuit before ball planting according to the present invention.

[0036] Figure 2 yes Figure 1 Schematic diagram of the 9 specific position points in the coordinate measurement step of the specific position points on the planted spherical surface.

[0037] Figure 3 yes Figure 1 Flowchart of the steps for determining the coordinates of key points in .

[0038] Figure 4 yes Figure 1 Schematic diagram of the extreme point projection model in the extreme point projection height simplification calculation step. DETAILED DESCRIPTION

[0039] like Figure 1 As shown, the method for estimating the coplanarity of a ball grid array package circuit before ball planting of the present invention is used to estimate the coplanarity value after a certain process before ball planting of a BGA package circuit. It includes the following steps:

[0040] S10. Coordinate measurement of specific position points on the ball implantation surface: measuring the vertical coordinates of 9 specific position points on the ball implantation surface of the packaged circuit; the 9 specific positions are respectively the center point of the packaged circuit, the 4 vertices of the packaged circuit, and the midpoint of the lines connecting the 4 vertices of the packaged circuit and the center point of the packaged circuit.

[0041] The positions of the 9 specific positions are as follows: Figure 2 As shown, the measured value of each point i is recorded as V Pi ,i=0,1~4,1'~4′.

[0042] S20. Determine the coordinates of key points: obtain the heights of the vertices and midpoints of each packaged circuit according to the height differences between the vertices and midpoints of each packaged circuit and the center point of the packaged circuit, select the midpoint of the packaged circuit vertex with the largest height difference as the extreme point, the packaged circuit vertex closest to the extreme point as the high-weight vertex, and the two packaged circuit vertices adjacent to the high-weight vertex as low-weight vertices.

[0043] like Figure 3 As shown, the step S20, determining the key point coordinates, includes:

[0044] S21, calculate the height of the non-center point: according to the four vertices P1, P2, P3, P4 of the package circuit, and the four midpoints P of the lines connecting the four vertices of the package circuit and the center point of the package circuit 1’ , P 2’ , P 3’ , P 4’The vertical coordinate of the package circuit center point is calculated to obtain the height of each non-center point, that is, each vertex and midpoint relative to the package circuit center point.

[0045] The non-center point height is calculated according to the following formula:

[0046] H Pi =V Pi -V P0

[0047] Among them, H Pi is the height of the non-central point Pi, V Pi is the vertical coordinate measurement value of the non-center point Pi, i = 1, 2, 3, 4, 1', 2', 3', 4', V P0 It is the vertical coordinate measurement value of the center point of the package circuit.

[0048] S22, determining the extreme point: subtracting the height of the midpoint closest to each vertex of the packaged circuit from the height of the vertex to obtain the warpage value of each vertex of the packaged circuit, and selecting the midpoint closest to the vertex with the largest warpage value as the extreme point.

[0049] In the step S22, the warpage value in the extreme point determination step is calculated according to the following formula:

[0050] W Pi =H Pi -H Pi′

[0051] Among them, W Pi is the warpage value of the package circuit vertex Pi, H Pi′ is the height of the midpoint, H Pi is the height value of the package circuit vertex Pi closest to the midpoint, i=1~4.

[0052] S23, high-weight vertex determination: select the vertex closest to the extreme value point as the high-weight vertex, and the height value of the high-weight vertex is used as the high-weight value;

[0053] S24, low-weight vertex determination: select two vertices adjacent to the high-weight vertex as low-weight vertices, and the height values ​​of the low-weight vertices are used as low-weight values.

[0054] S30, determining a reference plane: a plane is jointly determined by the high-weight vertex and the two low-weight vertices, and the plane is the reference plane.

[0055] Three reference points in space can determine a plane, so a reference plane can be determined using a high-weight vertex and two low-weight vertices.

[0056] S40, simplified calculation of the projection height of the extreme point: using a simplified formula to calculate the height of the projection point of the extreme point on the reference plane;

[0057] The step of simplifying the calculation of the extreme point projection height in S40 is specifically as follows:

[0058] The approximate height of the projection point of the extreme point on the reference plane is calculated according to the following simplified formula:

[0059] H S =(H H ×2+H L1 +H L2 )

[0060] Among them, H S is the simplified projection point height, H H is a high weight value, H L1 and H L2 are two low weight values.

[0061] The extreme point projection model is as follows Figure 4 As shown. Figure 4 The extreme point projection model shown can be used to obtain the simplified coordinate deviation e of the projection point on the reference plane as follows:

[0062] e=ll×cosθ

[0063] Among them, e is the simplified deviation value of the projection point coordinates, l is the length of 1 / 4 package diagonal, and θ is the angle between the straight line of the overweight point and the extreme point and the reference plane.

[0064] For actual packaged circuits, the angle is generally no more than 5°, so for a packaged circuit with a size of 60mm×60mm, the coordinate deviation between point Ps and the projection point of the extreme point on the reference plane is no more than 60μm according to the above formula. With such a small coordinate deviation, the height difference between the two points is no more than 5.5μm. For the estimated coplanarity of about 200μm, the estimated error is no more than 2.75%. So it can be used Figure 4 Ps in is used as the simplified projection coordinate, and the above simplified formula is used to calculate the approximate height of the projection point of the extreme point on the reference plane.

[0065] S50, coplanarity estimation: according to the height of the extreme point and the height of the projection point of the extreme point on the reference plane, a coplanarity estimation value is calculated.

[0066] The step S50, estimating the coplanarity, is specifically as follows:

[0067] The estimated coplanarity value is calculated as follows:

[0068] C=H Pi′ -HS

[0069] Where C is the coplanarity, H is Pt′ is the height of the extreme point, H S is the projection point height.

[0070] The present invention realizes the coplanarity estimation method of BGA packaged circuit before ball planting based on simplified algorithm model and simple measurement, provides effective means for circuit coplanarity evaluation before ball planting, and makes up for the lack of evaluation means in the current industrial equipment development window period. Estimating coplanarity data based on measured data of each state can effectively support the influence of each process on the degree of coplanarity change, and can be used to provide a basis for judging the influence of each link of the packaging process on the circuit coplanarity.

Claims

1. A method for estimating the coplanarity of a ball grid array package circuit before ball implantation, characterized in that: The steps include: Coordinate measurement of specific position points on the ball planting surface: measuring the vertical coordinates of 9 specific position points on the ball planting surface of the package circuit; the 9 specific positions are respectively the center point of the package circuit, the 4 vertices of the package circuit, and the midpoint of the lines connecting the 4 vertices of the package circuit and the center point of the package circuit; Determine the coordinates of key points: According to the height difference between each package circuit vertex and midpoint and the center point of the package circuit, obtain the height of each package circuit vertex and midpoint, select the midpoint with the largest height difference with the nearest package circuit vertex as the extreme point, the package circuit vertex closest to the extreme point as the high-weight vertex, and the two package circuit vertices adjacent to the high-weight vertex as low-weight vertices; Determine the reference plane: a plane is jointly determined by the high-weight vertex and the two low-weight vertices, and the plane is the reference plane; Simplified calculation of the projection height of the extreme point: using a simplified formula to calculate the height of the projection point of the extreme point on the reference plane; Coplanarity estimation: The coplanarity estimation value is calculated based on the height of the extreme point and the height of the projection point of the extreme point on the reference plane.

2. The coplanarity estimation method according to claim 1, characterized in that: The step of determining the extreme point comprises: Calculate the height of the non-center point: According to the four vertices P1, P2, P3, and P4 of the package circuit, and the four midpoints P of the lines connecting the four vertices of the package circuit and the center point of the package circuit 1’ , P 2’ , P 3’ , P 4’ The vertical coordinate of the package circuit center point is calculated to obtain the height of each non-center point, that is, each vertex and midpoint relative to the package circuit center point. The non-center point height is calculated according to the following formula: V Pi =V Pi -V P0 Among them, H Pi is the height of the non-central point Pi, V Pi is the vertical coordinate measurement value of the non-center point Pi, i = 1, 2, 3, 4, 1', 2', 3', 4', V P0 It is the vertical coordinate measurement value of the center point of the package circuit; Determination of extreme value points: The warpage value of each vertex of the package circuit is obtained by subtracting the height of the midpoint closest to the vertex from the height of each vertex of the package circuit, and the midpoint closest to the vertex with the largest warpage value is selected as the extreme value point; Determine high-weight vertices: select the vertex closest to the extreme point as a high-weight vertex, and the height value of the high-weight vertex is used as the high-weight value; Determine low-weight vertices: select two vertices adjacent to the high-weight vertex as low-weight vertices, and use the height values ​​of the low-weight vertices as low-weight values.

3. The coplanarity estimation method according to claim 2, characterized in that: The warpage value in the extreme point determination step is calculated according to the following formula: W Pt =H Pi -H Pt , Among them, H Pi is the warpage value of the package circuit vertex Pi, H Pi , is the height of the midpoint, H Pi is the height value of the package circuit vertex Pi closest to the midpoint, i=1~4.

4. The coplanarity estimation method according to claim 3, characterized in that: The simplified calculation steps of the extreme point projection height are specifically as follows: The approximate height of the projection point of the extreme point on the reference plane is calculated according to the following simplified formula: H S =(H H ×2+H L1 +H L2 ) Among them, H S is the simplified projection point height, H H is a high weight value, H L1 and H L2 are two low weight values.

5. The coplanarity estimation method according to claim 4, characterized in that: The coplanarity estimation step is specifically as follows: The estimated coplanarity value is calculated as follows: C=H Pi′ -H S Where C is the coplanarity, H is Pt′ is the height of the extreme point, H S is the projection point height.

Images