Electronic SMT manufacturing factory BGA rework operation pr

PCBA     |      2021-10-15 16:28

Table of content

1. Overview of Operation Guidance

2. Operation instructions

2.1 Definition

2.2 Purpose

2.3 Scope of application

2.4 Job responsibilities and special skills requirements

2.5 content

3. BGA rework process

3.1 Preparation before production

3.2 Remove BGA

3.3 Cleaning the pad

3.4 Coating accessories

3.5 Place BGA

3.6 Welding BGA

3.7 post-weld inspection

 

1. Overview of Operation Guidance

The operation process of the repair of leaded and lead-free single-board area array devices on the BGA assembly rework equipment and the matters needing attention in the repair process.

 

2. Operation instructions

2.1 Definition

BGA: A packaging form of integrated circuits, the input and output terminals (including solder balls, solder pillars, pads, etc.) are arranged in a grid on the bottom surface of the component. Including but not limited to PBGA, UBGA, WBGA, TBGA, CBGA and CCGA.

Lead-free BGA: BGA whose solder ball component is lead-free solder.

Sources of lead-free BGA information: For BGA chips with codes, PDM is used to confirm; for BGA chips whose device data cannot be found temporarily for new devices, the customer (person who needs to repair the single board) provides device information.

Mixed process: refers to the process of using leaded solder paste and lead-free BGA assembly.

2.2 Purpose

Instruct on-site operators how to select and call programs when using rework equipment to repair single-board area array devices with lead, hybrid, and lead-free processes, and standardize the operating methods and procedures of operators to ensure the quality of reworked single boards.

2.3 Scope of application

It is suitable for program selection, calling and repair operations when repairing array devices on single boards with leaded, mixed and lead-free processes, such as PBGA, QFP, PLCC, SOIC, CSP, and BGA sockets.

2.4 Job responsibilities and special skills requirements

Job responsibilities and special skills require maintenance operators to operate and maintain the equipment correctly, and fill in various relevant record forms.

Emergency troubleshooting. With skilled maintenance and operation skills, maintenance engineers have equipment troubleshooting, equipment parameter setting and management, and provide technical support for first-line production operation and maintenance, program modulation and planning management, and process technical support. Working principle and process of repairing equipment, debugging and repairing temperature curve

2.5 content

Rework tools, accessories and equipment

Rework tools: BGA rework station, electric chrome iron, scraper, small steel mesh, vacuum suction pen, scissors, tweezers, paintbrush (for solder paste application)

Accessories: Paste flux Alpha metals (no-clean LR721H2 HV); cleaning agent YC336 (for lead-free use), SC-10 (for lead-free use); absorbing braid; leaded solder paste (Sn63Pb37, NC-92J) ; Lead-free solder paste (Sn96.5Ag3.0Cu0.5); Broken white cloth

Rework equipment SV-550 rework station

The RD-500 rework station has 3 heating systems, among which the upper and lower ones that accurately heat the target chip and circuit board are hot-air heating. The third is a regional heating element that gradually heats the entire printed circuit board from the bottom. SV-550 needs to be equipped with hot air nozzles of different sizes to repair different devices.

 

3. BGA rework process

3.1 Preparation before production

A. Single board baking preparation and related requirements:

1) According to the different exposure time, the veneers are given different baking requirements,

Veneer exposure time: Based on the processing month time on the bar code of the veneer made of the veneer, the veneer in the current month is 1 month by default, and so on.

2) Baking time

SMT repaired single board is less than 24 hours by default, and it can be done without baking. BGA assembly repair is completed within 10 hours after receiving the single board.

Special veneers, special needs of repair personnel, such as device analysis, etc.; feedback process personnel to give baking requirements

B. Precautions for inspection and preparation before board rework

1) Check whether there are gussets and rework chips on the veneer (the rework surface and back of the veneer) and there are devices with a height of more than 20mm (as long as it interferes with the hot air nozzle) within 10mm, and the gusset and the devices that interfere with the rework must be disassembled Can be repaired;

2) If there are optical fibers on the front and back of the reworked veneer, and the battery in the accessory area needs to be removed, it can be reworked;

3) If there are radiators, plug-in crystal oscillators, electrolytic capacitors, plastic light guides, non-high temperature barcodes, BGA, BGA sockets, and through-hole plastic components such as plastic connectors, the surface of the reworked veneer must be 10mm and 10mm away from the reworked chip. It can be repaired after sealing with 5-6 layers of high temperature adhesive paper. If it is within 10mm, you need to remove the corresponding device (except BGA) before it can be repaired;

4) Other BGA and other chips and plastic packaged devices that may be affected by heat after being repaired need to be heat-insulated.

When the above 4 situations involve the disassembly and assembly of related components, the sender should disassemble it by himself, and then send it to the BGA repair section for repair, otherwise, the heat damage caused by the device will be handled by the sender.

C. Determination of repair accessories

1) When the parts to be repaired are CCGA, CBGA, BGA, and the solder ball material is not 63/37 solder material, the printed solder paste method must be used for repair. The type of solder paste is selected according to the solder paste specified in the operating instructions of the model

2) When it is 63/37 solder material, it can be soldered with flux paste or printed solder paste; when solder paste is used, a small stencil corresponding to the device pad should be used for tin printing. The type of solder paste is selected according to the solder paste specified in the operating instructions of the model, and the soldering paste uses ALPHA soldering paste LR721H2, 100g/bottle

3) For the rework of lead-free devices, for BGAs smaller than 15*15mm, solder paste can be used for soldering. Other large-size BGAs must be soldered by brushing solder paste. The type of solder paste is selected according to the solder paste specified in the operating instructions of the model, and the soldering paste uses ALPHA soldering paste LR721H2, 100g/bottle

D. Repair equipment and other requirements

1) Before repairing, if the equipment has not been heated for more than 30 minutes, the equipment must be preheated. Warm-up procedure can be any repair procedure

2) Single board positioning and support

The position of the support rods: the support rods should be distributed as symmetrically as possible (as far as possible to make the veneer heated evenly as a principle), and should not touch the bottom device. The position of the support rod is preferably located in the middle of the PCB board, so that the PCB remains flat and cannot be supported on the device, and the buckle is fastened and the positioning pin is locked. For smaller PCBs, you can use a rotating support block 90 degrees to fix it.

3) Selection and replacement of heating nozzles

i. Choose the nozzle whose actual size is 2~5mm larger than the BGA. Pay attention that the nozzle can not damage the surrounding components. After using the nozzle, put it back on the corresponding position of the tooling rack.

Replacement of nozzle: Take the nozzle body and turn 30 degrees to replace the nozzle on the heating element. Note that when replacing the upper nozzle, you must not pull it out forcefully to avoid damaging the vacuum suction rod and the connected silicone nozzle and gasket.

Electronic SMT manufacturing factory

3.2 Remove BGA

Place the reworked single board on the rework station, and select the corresponding rework procedure from the BGA assembly removal procedure catalog corresponding to each device to heat the BGA. After the program runs, remove the device from the rework station.

1) When there is a program corresponding to the board name in the program library, the program with the same board name is preferred.

Generally, the corresponding repair procedure can be selected according to the size and size of the BGA. (Refer to item 5.3-BGA dismantling/welding procedure selection correspondence table for rework procedures)

2) After the repair procedure is completed, the device will automatically pick up the removed device. When the device surface is rough and uneven, it is allowed to use tweezers to pick it up; when using tweezers to pick it up, first use tweezers to gently move the device to make sure that the device is completely melted. Pick up immediately.

3) After disassembling the device and before cleaning the pad, check whether the pad of the removed device has any defects such as falling or damage to the pad. If there is any abnormality, feedback the engineer to deal with it.

3.3 Cleaning the pad

Place the veneer on the workbench and use a soldering iron and a soldering rope to suck away the excess residual tin on the pad to level the pad.

When cleaning, place the suction wire on the pad, lift the suction wire up with one hand, and place the soldering iron on the suction wire with the other hand, lightly press the soldering iron to melt the residual solder on the BGA pad and absorb it to the suction wire , And then move the suction line to another position to suck the remaining part of the solder, and can’t forcefully drag on the pad to avoid damage to the pad.

Leaded device pad cleaning, soldering iron temperature <actual value>340+/-40℃; Lead-free device pad cleaning, soldering iron temperature <actual value>370+/-30℃; for CBGA, CCGA pad cleaning, soldering iron temperature Set <actual value> 400+/-30℃. After cleaning, use a cleaning agent to remove solder residues and foreign substances on the devices and PCB pads. After cleaning, check the devices and PCB pads with a 20X-50X magnifying glass, whether there are defects such as scratches, peeling damage, etc.; if A feedback engineer will deal with it.

3.4 Coating accessories

According to the third point in 001, determine whether to use tin printing or brushing solder paste for rework. The methods of printing solder paste and brushing solder paste are as follows.

(1) Brushing solder paste:

Dip a small amount of flux paste with a paintbrush, and apply lightly back and forth on the pad.

Check the application of the solder paste on the pad, and the solder paste is required to be evenly spread. There must be no accumulation of solder paste on the board.

Check the veneer pad where the flux paste has been applied. There should be no fiber or hair residue; if necessary, clean it again and apply it again.

(2) Printing solder paste

Select the corresponding tin-printed stencil, position the small tin-printed stencil and stick it on the PCB with tape (to fix the stencil and prevent the solder paste from overflowing); pay attention to the need to make the stencil opening and the pad completely overlap, and it is in a good position.

Use a scraper to take a proper amount of solder paste, and then scrape it on a small steel mesh. When scraping the solder paste, try to make the solder paste roll between the steel mesh and the squeegee.

Slowly lift the steel mesh upwards with your hand or a tool, and reduce the shaking of your hands during the extraction process.

Visually inspect the quality of the printed tin and whether there is tin splashing around it, and see whether the pad has any defects such as missing printing, continuous tin, little tin, sharpening, and misalignment. (Picture 10) If there is, it is necessary to clean the pads with washing water, and reprint after the washing water evaporates.

Clean the stencil and scraper, put it back in place, and use it next time.

Stencil coating solder paste

Remark:

1. In view of the dense layout and the small steel mesh cannot be placed on the PCB, the method of printing tin on the device can also be used. Place the ball-planting steel mesh on the BGA ball. The method of printing solder paste is the same as that on the PCB. Be careful to avoid damaging the BGA.

2. The use of printed solder paste, solder paste, environmentally friendly water for cleaning and other auxiliary materials refer to the “Regulations for the Use of Maintenance Accessories” and record them in the corresponding bad board bar code.

3.5 Place BGA

1) Place the veneer coated with auxiliary materials on the workbench steadily, and evenly support the bottom of the veneer (specifically set according to the veneer positioning and support requirements in 001 pre-production preparation). Start the image alignment system, place the device on the suction nozzle in the nozzle of the machine, make the image of the device and the pad overlap, and run the machine to complete the placement action. (For specific steps, please refer to “RD-500 Operating Regulations”)

Before attaching the BGA, check the code and direction of the BGA to be consistent with the maintenance veneer; check whether the solder balls of the BGA device are abnormal, such as the size of the solder balls, the lack of balls, and the irregular shape of the solder balls.

2) When placing the device, you must carefully observe and adjust to make the device image and the pad image completely overlap, or check that the device silk screen frame is flush with the device.

When using tin-printed rework, the BGA must be placed on the PCB with equipment, and manual placement is not allowed.

When using brush-assisted solder paste to rework, you can place the device manually. Ordinary veneers should be aligned with the silk-screen frame; if they are non-screen-printed veneers, they should be aligned with the etched frame on the opposite corner of the pad; for veneers without any frame markings, machine alignment and patching must be used .

3) After the device is placed, it is necessary to check whether the height of the repaired device is the same, whether the height is uneven, the device is tilted and other abnormalities.

3.6 Welding BGA

First, set up the support and position the PCB according to the single board positioning and support requirements in the preparation of 001 before production. After the position is determined, call the corresponding program from the soldering BGA assembly program catalog of each device to heat the BGA. The program is completed and the device is completed The welding process. After the veneer cools down, remove the PCB.

Note that during the operation, pay close attention to the welding of the veneer. If there are abnormalities such as scorching or severe deformation, the machine should be stopped immediately, the site should be kept, and the engineer should be reported to deal with it. The same PCB board can be repaired up to 3 times, and the same BGA board can be repaired up to 2 times.

3.7 post-weld inspection

After the welding is completed, the veneer needs to be inspected. Focus on the following items:

1) Visually inspect the solder joints around the BGA to see if there are defects such as false soldering, continuous tin, and tin beads on the back. After confirming that there is no welding quality problem with X-Ray (3D microscope can be used to check the welding status if necessary), the next veneer can be reworked or handed over to the next process.

2) Check whether there is tin splashing or other defects around the soldered device, and check whether there are CHIP parts on the back of the veneer that are crushed by the thimble.

3) Clean the excess flux residue around the BGA assembly with plate washer water.