PCBA quality control

preface

The general specification includes three documents: PCBA quality control - layot

PCBA quality control - SMT

PCBA quality control - PCBA commissioning

This specification mainly controls the quality tracking and improvement of SMT link

This specification is applicable to the improvement of SMT qualification rate of our company,

Especially for small quantity, variety and high quality products

This specification is proposed by R & D hardware department.

1、 Steel mesh

1. The expansion of modular steel mesh can't simply extend the four sides of pad symmetrically, and the internal expansion has been considered in pad design. If the tin effect of some large module pads is not good and the tin content needs to be increased, the tin amount should be added from the opening of the pad direction which will not be squeezed by the module, so as to prevent the internal short circuit of the module or the generation of excess solder beads. (2G module, 3G module, u-blox module, Bluetooth module, large inductance and capacitance, etc.)

As shown in the figure:

2. The opening of BGA steel mesh needs to be adjusted reasonably according to the size and gap of BGA chip pin sphere, and the reasonable value should be adjusted between false soldering and short circuit. Our products have many BGA package specifications, so we must refer to the chip condition and can not be handled according to the general situation (the recommended opening ratio is 88% - 95%)

2、 Solder paste

According to the previous experience, there are some different quality problems in different batches of the same steel mesh and the same plate, so the solder paste link needs to be paid attention to

1. Solder paste must be used up within 24 hours after unsealing. If it cannot be used up, it will be scrapped

2. It is forbidden to take the sealed solder paste to the refrigerator for further use after freezing, so that one tin paste corresponds to one batch

3. Take out the unopened solder paste from the refrigerator, return the temperature to more than 5 hours, and put the solder paste upside down. At the same time, add the storage and temperature recovery area, record the starting time of temperature recovery, and label it.

4. Hand stir solder paste must be sufficient (more than 5 minutes or more than 100 times)

5. Labeling and finishing of scrap solder paste. Since the single pot of batch pastes can not be used in time, the scrap of completely finished solder paste shall be borne by our company. It is forbidden to use expired solder paste for the reason of saving.



3、 Reflow soldering


1. Our products require the furnace temperature curve to have the specified value, and issue the furnace temperature curve chart of each product, which is convenient to adjust the furnace temperature curve value according to the quality situation

2. Generally, the temperature of lead-free furnace is different from that of lead-free furnace, and the temperature of large and thick plate and small and thin plate furnace is also different. Try not to share the same furnace with different plates at the same time. As SMT scheduling, the rationality of sharing reflow furnace for multiple lines should also be considered. This is also a place where some quality problems are easy to be ignored.


4、 Custom documentation

Documents related to PCBA commissioning Department

1. "Reflow furnace temperature curve table" -- corresponding to each batch of plates, the implementation of random inspection by our engineering personnel

2. QC inspection record form

Record the defect rate of batches

Record the defective points in detail (we provide the label paper, label the number after passing through the furnace, and record the PCBA board in question). We pay for the extra labor cost

3. "PCBA debugging abnormal feedback form" - provided by our company, the chip factory is responsible for handling and solving problems and formulating improvement plans


5、 Material


Material preparation related to business

1. In order to prevent the first part of equipment debugging from being stained with glue, resulting in poor welding, PCBA and IC board with adhesive tape are recycled to our company for filing or maintenance (large and short module IC can be used cautiously after cleaning, and BGA chip is forbidden to be used again)

2. Our company's PCB and materials provide debugging equipment loss materials (the risk of PCB cleaning with solder paste repeatedly in the debugging stage is also very high)

3. The reusable chip / PCB loss of debugging equipment is recoverable loss, and the non recoverable loss needs to be calculated separately.