CN113660790B

CN113660790B - Method for poor solder mask development by laser ablation rework

Info

Publication number: CN113660790B
Application number: CN202110931752.XA
Authority: CN
Inventors: 许伟廉; 陈世金; 巫萃婷; 梁鸿飞; 郭茂桂; 冯冲; 韩志伟
Original assignee: BOMIN ELECTRONICS CO LTD
Current assignee: BOMIN ELECTRONICS CO LTD
Priority date: 2021-08-13
Filing date: 2021-08-13
Publication date: 2022-09-13
Anticipated expiration: 2041-08-13
Also published as: CN113660790A

Abstract

The invention discloses a method for reworking solder mask poor development by laser ablation, relates to printed circuit board processing, and solves the technical problem of high product rejection rate caused by the influence on the product quality due to traditional manual scraping or liquid medicine cleaning. And optimizing the poorly developed bonding pad and filling an ablation point to obtain a laser drilling program, and ablating the ink on the surface of the bonding pad according to the laser drilling program. The invention has higher precision and better consistency, can reduce the rejection rate of products and create better benefits.

Description

Method for poor solder mask development by laser ablation rework

Technical Field

The invention relates to printed circuit board processing, in particular to a method for reworking solder mask poor development by adopting laser ablation.

Background

In the solder mask process, the circuit board may have the following quality abnormal points, such as incomplete development, poor exposure, excessive development, film printing, ink waste and the like. At present, the pads with local poor development caused by small windows or poor vacuum suction are manually processed, and ink on the pads is scraped off by a scalpel. However, the method has the problems of low efficiency and low success rate, which often results in product scrapping and increases production cost. If the nickel-gold alloy is not treated, the problems of no nickel-gold deposition and poor welding exist, and the product is scrapped. Can certainly go on through special oil removal liquid medicine and move back washing board face china ink, then weld printing ink is hindered to silk screen printing again, but printing ink can hardly move back and wash after the high temperature curing, and the base material that the circuit board was used can cause the product harmomegathus to be unusual through moving back long-time high temperature soak of oil liquid medicine, attack, influences follow-up production quality, and the base material blurs out when serious, influences CAF reliability, the heat-resisting reliability etc. of product to cause the visitor to complain, bring harmful effects such as claim.

Disclosure of Invention

The invention aims to solve the technical problem of the prior art, provides a method for improving poor solder mask development by laser ablation rework, and solves the problem of high product rejection rate caused by influence on product quality due to traditional manual scraping or liquid medicine cleaning.

The method for the reworking solder mask poor development by laser ablation optimizes a pad with poor development and fills ablation points to obtain a laser drilling program, and ablates ink on the surface of the pad according to the laser drilling program.

The optimization of the poor-developed bonding pads specifically comprises,

comparing the areas of the welding pad and the resistance welding windowing window, and if the areas of the welding pad and the resistance welding windowing window are consistent, performing deviation shrinkage prevention on the resistance welding windowing window to obtain a laser ablation working area; if the solder mask window is larger than the bonding pad, the size of the solder mask window is reduced to be consistent with the designed size of the bonding pad, and then the bias shrinkage prevention is carried out on the solder mask window to obtain a laser ablation working area.

The deviation prevention shrinkage is specifically that the edge of the solder mask windowing is inwards retracted by 10um-20 um.

And filling ablation points in the poorly developed bonding pad, specifically, filling a laser ablation working area in a maximum area array sequencing mode through the ablation points to obtain the laser ablation working area with the maximum area after filling, and simultaneously recording the path of the ablation points to obtain a laser drilling program.

The maximum area array ordering, specifically,

uniformly tiling ablation points by taking the edge of the laser ablation working area as a boundary, and carrying out multiple times of ablation point tiling operation along the boundary, and simultaneously ensuring that the maximum non-overlapping area of each ablation point can be ablated;

and secondly, taking the edge of an inner ring surrounded by ablation points close to the center of the laser ablation working area as a boundary, and continuing the tiling operation of the ablation points until the laser ablation working area is filled with the ablation points.

After the laser drilling program is obtained, the CCD of the laser drilling machine is adopted to grab the four foolproof points with the same size, and the printed circuit board to be reworked is subjected to automatic expansion, contraction, stretching and compensation so as to identify the laser ablation working area and the initial position of the ablation points.

Before the ink on the surface of the bonding pad is ablated, ablation parameters are set according to the residual quantity of the ink on the bonding pad.

And after the ink on the surface of the bonding pad is ablated, cleaning the carbide on the bonding pad.

When the printed circuit board has poor development, firstly adopting an appearance inspection machine to screen out the abnormal bonding pads, and then marking the bonding pads and the serial numbers of the printed circuit board.

Advantageous effects

The invention has the advantages that:

1. through the printing ink on the bad pad of laser ablation development, compare with traditional manual scraping or liquid medicine washing, its precision is higher, the uniformity is better, can reduce the disability rate of product, creates better benefit.

2. The solder mask windowing is prevented from deflecting and contracting, ink on the edge of the solder mask windowing can be effectively prevented from being ablated due to laser beam deflection, or the bottom base material on the edge of a bonding pad is burnt, the integrity of the printed circuit board is ensured, and the reworking qualification rate of the printed circuit board is improved.

Drawings

FIG. 1 is a schematic flow chart of the present invention;

FIG. 2 is a schematic diagram of a laser ablation working area configuration with a pad consistent with a solder mask window of the present invention;

FIG. 3 is a schematic diagram of a laser ablation working area configuration when the solder mask window is larger than the pad of the present invention;

FIG. 4 is a first state diagram of the tiling of ablation spots in a laser ablation working area of the present invention;

FIG. 5 is a second state diagram of the tiling of ablation spots in a laser ablation working area of the present invention

FIG. 6 is a third state diagram of the tiling of ablation spots in a laser ablation working area of the present invention;

FIG. 7 is a fourth state diagram of the tiling of ablation spots in a laser ablation working area of the present invention;

fig. 8 is a fifth state diagram of the tiling of ablation points in the laser ablation working area of the present invention.

Wherein: 1-bonding pad, 2-resistance welding windowing, 3-laser ablation working area and 4-ablation point.

Detailed Description

The invention is further described below with reference to examples, but not to be construed as being limited thereto, and any number of modifications which can be made by anyone within the scope of the claims are also within the scope of the claims.

Referring to fig. 1, the method for reworking solder mask poor development by laser ablation specifically comprises the following steps:

firstly, when the pad 1 of the printed circuit board is poor in development, firstly, an appearance inspection machine is adopted to screen out the abnormal pad 1, and then the numbers of the pad 1 and the printed circuit board are marked, so that the abnormal pad 1 can be conveniently and quickly positioned and the data of the printed circuit board can be conveniently and quickly read.

And step two, acquiring the information of the printed circuit board required in the rework process according to the serial number of the printed circuit board in the step. The printed circuit board data mainly comprises four fool-proof points with the same size in the printed circuit board and used as positioning points; and copying the corresponding solder mask window 2 in the printed circuit board material and the designed pad 1 data according to the marked pad 1.

And step three, after the copying of the printed circuit board data is finished, optimizing the poor-developed bonding pad 1 and filling the ablation point 4 to obtain a laser drilling program.

Wherein, the poor developing pad 1 is optimized, specifically including,

the area of pad 1 and its solder resist window 2 are compared. If the areas of the pad 1 and the solder resist window 2 are the same, the solder resist window 2 is subjected to bias shrinkage prevention to obtain a laser ablation working area 3, as shown in fig. 2. As shown in fig. 3, if the solder resist window 2 is larger than the pad 1, the size of the solder resist window 2 is reduced to be consistent with the designed size of the pad 1, and then the offset shrinkage prevention is performed to obtain the laser ablation working area 3. Prevent partially contracting to hindering and weld windowing 2, mainly be in order to prevent to weld the in-process of 1 ablating of pad, prevent that laser beam off normal from leading to ablating the printing ink that hinders and welds 2 edges of windowing, or burn the problem of the bottom substrate at 1 edges of pad, can effectually ensure printed circuit board's integrality, improve the qualification rate of doing over again.

Preferably, the deviation shrinkage prevention is to inwardly retract the edge of the solder resist opening window 2 by 10um to 20 um. In general, the greater the edge setback, the less affected the laser beam deflection. However, too much retraction will result in too small a laser ablation working area 3, which is not conducive to later welding. Therefore, the retraction range is set between 10um and 20um, the influence caused by laser ablation deviation is reduced, and the problem that the normal processing cannot be carried out in the later period due to the fact that the windowing area of the bonding pad 1 is too small is solved.

In the step, the pad 1 with poor development is filled with ablation points 4, specifically, the method comprises the steps of filling the laser ablation working area 3 in a maximum area array sequencing mode through the ablation points 4 to obtain the laser ablation working area 3 with the maximum area after filling, and simultaneously recording the path of the ablation points 4 to obtain a laser drilling program.

In order to ensure the stability during ablation and prevent the laser deviation from being too large, the ablation process needs to be performed in a jogging mode. In the embodiment, the laser ablation working area 3 is filled in the maximum area array sorting mode, so that the working path of laser ablation can be effectively obtained, meanwhile, the condition that the edge of the laser ablation working area 3 is similar to a straight edge can be well ensured, and the ablation integrity is ensured.

With respect to the maximum area array ordering, specifically,

in the first step, the ablation points 4 are uniformly tiled by taking the edge of the laser ablation working area 3 as a boundary, and the tiling operation of the ablation points 4 is carried out for a plurality of times along the boundary, and simultaneously, the non-overlapping area which can be ablated by each ablation point 4 is maximized.

The determination mode of the maximum non-overlapping area that can be ablated by each ablation spot 4 can be determined by the following method. For two adjacent ablation points 4, the center point of the ablation point 4 and the intersection point of the ablation point 4 and the boundary can be connected, so as to obtain a symmetrical point of the two connection lines. And connecting the central points of the two ablation points 4, and taking the middle point of the connecting line as another symmetrical point, thereby determining the symmetrical line of the two adjacent ablation points 4. When the ablation points 4 are laid flat, the edge of the ablation point 4 is contacted with the limit, then the ablation point 4 is moved, when the central point of the ablation point 4 is positioned on the symmetrical line, the movement of the ablation point 4 is stopped, thereby realizing the laying operation of the ablation point 4, and the non-overlapping area which can be ablated by the ablation point 4 is the largest.

And secondly, taking the edge of an inner ring surrounded by the ablation points 4 close to the center of the laser ablation working area 3 as a boundary, and continuing the tiling operation of the ablation points 4 until the laser ablation working area 3 is filled with the ablation points 4.

The maximum area array ordering is described below with respect to fig. 4-8. Assuming a selected laser beam diameter of 0.1mm, a first ablation spot 4 is placed on the edge of the laser ablation working area 3 as shown in fig. 4, and this spot is used as the initial position for ablation. As shown in figure 5, the edge of the laser ablation working area 3 is tiled through four ablation points 4 to complete the first tiling effect, and the ablation points 4 are not overlapped, so that the maximum area can be ablated. As shown in fig. 6, the ablation points 4 are sequentially inserted between two adjacent ablation points 4, and a total of four ablation points 4 are inserted, so as to ensure that the maximum non-overlapping area that can be ablated by the ablation points 4 is achieved. That is, the positional relationship between the four ablation spots 4 and the original four ablation spots 4 can be considered as 45 ° rotation of the original four ablation spots 4. I.e. the ablation spot 4 is ablated to the maximum area of the laser ablation work area 3 that has not been ablated. As shown in fig. 7, the ablation spots 4 are further tiled, and a total of eight ablation spots 4 are inserted, and the eight ablation spots 4 can be considered to be formed by 22.5 ° rotation of the original eight ablation spots 4. The edge of the resulting ablated area is approximately the edge of the laser ablated working area 3. However, if a large unfilled area still exists between the outer edge of the ablation area formed by the ablation spots 4 filling and the edge of the laser ablation working area 3, tiling should continue using the ablation spots 4. Finally, as shown in fig. 8, the unfilled position in the middle of the laser ablation working area 3 can be filled directly through the ablation point 4. If the diameter of the laser ablation working area 3 is too large, filling can be achieved by means of multilayer filling. In this embodiment, the filling path of the ablation point 4 is the laser drilling program.

And step four, after the laser drilling program is obtained, the CCD of the laser drilling machine is adopted to grab the four foolproof points with the same size, and the printed circuit board to be reworked is automatically expanded, contracted, stretched and compensated so as to identify the initial positions of the laser ablation working area 3 and the ablation points 4.

And step five, before the ink on the surface of the bonding pad 1 is ablated, setting ablation parameters according to the residual quantity of the ink on the bonding pad 1. In this example, a 2.0-2.5MARK aperture is used, laser energy is set to 0.2-0.5mj, wavelength is set to 1-3 μ s, and the number of guns is set to 1-3. However, the specific parameter setting is determined according to the residual amount of ink on the surface of the bonding pad 1.

Specifically, if no obvious ink residue exists on the surface of the bonding pad 1 and the ink is transparent, a parameter with a lower numerical value is preferentially selected from the parameters for operation; if slight ink residue exists on the surface of the bonding pad 1 and the ink is light color, the parameters with numerical values in the middle section are preferably selected from the parameters for operation; if there is obvious ink residue on the surface of the bonding pad 1 and the ink is in a darker color, the parameter with a higher value should be selected to perform the operation.

When setting parameters, such as laser energy, etc., too high, although ink on the surface of the pad 1 can be completely removed, there is a risk of damaging copper, and the post-processing is difficult with severe carbonization. If the parameter is set too low, the ink on the surface cannot be removed, and the rework is not successful.

It should be noted that, due to the difference of the equipment environment, the present embodiment does not limit the above parameters, and during ablation, fine adjustment can be performed according to the actual situation.

And step six, ablating the ink on the surface of the bonding pad 1 according to a laser drilling program so as to complete the ablation of the ink on the bonding pad 1.

And step seven, after the ink on the surface of the welding pad 1 is ablated, cleaning the carbide on the welding pad 1 to finish cleaning the ink on the welding pad 1. Compared with the traditional manual scraping or liquid medicine cleaning mode, the mode of removing ink on the welding disc 1 through laser ablation has the advantages of higher precision and better consistency, can reduce the rejection rate of products, and creates better benefits.

And step eight, performing FQC return inspection.

And step nine, carrying out the surface treatment process again, or protecting the reworked bonding pad 1 by adopting a manual gold spotting method. And finally finishing the whole rework process.

The above description is only a preferred embodiment of the present invention, and it should be noted that those skilled in the art can make various changes and modifications without departing from the structure of the present invention, which will not affect the effect of the implementation of the present invention and the practicability of the patent.

Claims

1. A method for reworking solder mask poor development by laser ablation is characterized in that a pad with poor development is optimized and ablation points are filled to obtain a laser drilling program, and ink on the surface of the pad is ablated according to the laser drilling program;

the optimization of the poor-developed bonding pads specifically comprises,

comparing the areas of the welding pad and the resistance welding windowing window, and if the areas of the welding pad and the resistance welding windowing window are consistent, performing deviation shrinkage prevention on the resistance welding windowing window to obtain a laser ablation working area; if the solder mask window is larger than the bonding pad, reducing the solder mask window to be consistent with the designed bonding pad in size, and then performing deviation shrinkage prevention on the solder mask window to obtain a laser ablation working area;

filling ablation points in a pad with poor development, specifically, filling a laser ablation working area in a maximum area array sequencing mode through the ablation points to obtain the laser ablation working area with the maximum area after filling, and simultaneously recording the path of the ablation points to obtain a laser drilling program;

the maximum area array ordering, specifically,

uniformly tiling ablation points by taking the edge of the laser ablation working area as a boundary, and continuously performing multiple tiling operations between two adjacent ablation points along the boundary in sequence, wherein the non-overlapping area which can be ablated by each ablation point is maximized;

and secondly, with the edge of an inner ring surrounded by ablation points close to the center of the laser ablation working area as a boundary, continuing the tiling operation of the ablation points in the tiling mode in the first step until the laser ablation working area is filled with the ablation points.

2. The method for reworking poor solder mask development by laser ablation according to claim 1, wherein the partial shrinkage prevention is realized by inwardly retracting the edge of the solder mask opening window by 10-20 um.

3. The method as claimed in claim 1, wherein after the laser drilling program is obtained, the CCD of the laser drilling machine is used to capture four foolproof spots with the same size, and the printed circuit board to be reworked is automatically stretched and compensated for expansion and contraction to identify the laser ablation working area and the initial position of the ablation spot.

4. The method for defective solder mask development by laser ablation rework according to claim 1, wherein before the ablation of the ink on the surface of the bonding pad, the setting of ablation parameters is performed according to the residual amount of the ink on the bonding pad.

5. The method for defective solder mask development by laser ablation as claimed in claim 1, wherein the carbide on the pad is cleaned after the ink on the pad surface is ablated.

6. The method for defective development of solder mask reworked by laser ablation according to claim 1, wherein when the printed circuit board has defective development, the pads with abnormal development are screened out by an appearance inspection machine, and then the numbers of the pads and the printed circuit board are marked.