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Frequently Asked Questions about PCB Model Making
- 2020-01-30-

Semi-finished circuit boards of electronic products after reflow soldering due to various reasons (reflow soldering equipment reasons, circuit board reasons, worker operation reasons, solder paste reasons, placement machine reasons, etc.) often see some products appear different This kind of undesirable phenomena, if the occurrence of these undesirable phenomena is not strictly controlled, the company will be exposed to serious consequences. Below, I will make a detailed analysis of the common problems of PCB model making and propose corresponding preventive solutions The method, hope to give some help to electronic product manufacturers. Welding defects of electronic products are divided into major defects, minor defects and surface defects.

Any defect that makes the SMA function of an electronic product fail is called a major defect; a minor defect means that the wetting between the solder joints is still good, which will not cause the loss of the SMA function of the electronic product, but there are possible defects that affect the life of the product; surface defects refer to Does not affect the function and life of the product.

PCB样板打板常见问题解答

In the process of research and production of PCB prototypes, we know that reasonable surface assembly technology plays a vital role in controlling and improving the quality of PCB prototypes.

Reflow soldering is also an important part of the PCB prototype boarding process, but in actual operation, we often see that there are many small CHIP components, especially chip resistors, which will cause the chip components to be unsoldered and erected This kind of defect is vividly referred to as the phenomenon of "stone erection" in the process of making PCB prototypes. After the PCB circuit board passes through the reflow oven, small patch components on the circuit board are often erected. The proper term for our PCB prototype boarding is called component tombstone. In particular, chip resistors often have a "tombstone" phenomenon.

1. Analysis of tombstone phenomenon:

In reflow soldering, chip components often stand up. The reason: the root cause of the tombstone phenomenon is that the wetting force on both sides of the component is unbalanced, so the torque at both ends of the component is not balanced, which leads to the tombstone phenomenon. happened.

The following conditions will cause the wetting force on both sides of the component to be unbalanced during reflow soldering:

1.1. The pad design and layout are unreasonable. If the pad design and layout have the following defects, it will cause the wetting force on both sides of the component to be unbalanced.

1.1.1. One of the pads on both sides of the component is connected to the ground or the area of ​​one side of the pad is too large, and the heat capacity at both ends of the pad is uneven;

1.1.2 The temperature difference across the PCB surface is too large to cause uneven heat absorption on both sides of the component pad;

1.1.3, large devices QFP, BGA, small chip component pads around the heat sink will have uneven temperature at both ends.

Solution: Change the pad design and layout.

1.2. There is a problem with the printing of solder paste and solder paste. The activity of the solder paste is not high or the solderability of the component is poor. After the solder paste is melted, the surface tension is different, which will cause the pad wetting force to be unbalanced. The solder paste printing of two pads The amount is uneven, and the more side will absorb more heat due to the solder paste, and the melting time will lag, so that the wetting force will be unbalanced.

Solution: Choose a solder paste with higher activity to improve the solder paste printing parameters, especially the window size of the template.

1.3. The uneven force in the Z-axis direction of the patch shift will cause the uneven depth of the component immersed into the solder paste, and the wetting force on both sides will be unbalanced due to the time difference during melting. If the component is shifted, it will directly cause Stele.

Solution: Adjust the process parameters of the placement machine.

1.4. The furnace temperature curve is incorrect. If the reflow furnace body is too short and the temperature zone is too small, the working curve of the PCB heating will be incorrect, so that the humidity difference on the board surface is too large, resulting in an unbalanced wetting force.

Solution: Adjust the appropriate temperature curve according to each different product.

1.5. The oxygen concentration in nitrogen reflow soldering. Nitrogen protection reflow soldering will increase the wetting force of the solder, but more and more examples show that the phenomenon of tombstones when the oxygen content is too low increases; it is generally believed that the oxygen content It is most appropriate to control it to the minus 6 power of (100~500)×10.

Precautions for each stage of PCB model boarding and patch welding processing:

The batch size is generally below 100PCS. It has never been produced before. The focus is on verifying the mass production of the model. The production of PCB prototypes of such models must pay attention to the following things:

Precautions for production during the trial production stage of PCB prototypes:

1. Preparation of PCB model board:

A. After learning from PMC or the purchasing office that a certain model is ready for trial launch, you must know the person in charge of the development of the model and the person in charge of the biotechnology model in order to obtain relevant resources and help in the future;

B. Borrow a prototype: I need to have a simple understanding of the relevant functions of the machine produced, and I have a good product to test the full function of the finished machine several times;

C. Understand all the post-welding components of the model, plan the post-welding process, evaluate the post-welding operation and post-welding precautions;

D. Understand the use of test fixtures (the first trial production often does not have test fixtures), and plan test items and processes;

E. Understand the component layout of the entire PCB, and evaluate the characteristics of certain components.

F. The PCB template printing materials that biotechnology needs to prepare include "component location diagram", "BOM table" and "principle diagram". These materials must be the same version as the produced PCB;

G. It is best to prepare a sample before departure;

2. Confirmation of materials in the PCB prototype making factory: The preparation and distribution of biotechnology cannot interfere, but after sending out several confirmations, it is best to confirm with the development engineer:

A. First understand the situation of material preparation, whether the material is complete will determine the production arrangement, and if the material is not complete, it should be reported to the factory immediately;

B. Confirmation of key materials, such as the version and material number of major materials such as FWIC, BGA, PCB board, etc.; material confirmation must check the BOM;

C. The general manufacturer's IQC and material staff will also check the materials. If there are any inconsistent materials, they should immediately check with the development engineer;

3. First article confirmation:

A. Confirm the first piece of the patch, pay attention to the direction and specifications of the main components, check the first piece record of the PCB model maker, and check the model at the same time;

B. After the furnace, the PCB needs to see the tin consumption of each component and the temperature resistance of the components;

C. It is best to work on the first post-welding part by yourself, and the development engineer will confirm it; at this time, start preparing for the post-welding process and post-welding SOP;

D. If there is a test fixture, test the first piece by yourself, and the development engineer confirms the test item, and starts to prepare the test item and test SOP;

4. Problem tracking and confirmation:

Record and sort out the problem points that occurred during the entire production process, including data, materials, placement, post-welding, testing, maintenance, and other problems in the PCB prototype production process, and summarize it into a problem tracking report, and print it with the PCB prototype in time. The person in charge of board production and the engineer of the development department confirm the problem.

5.Information feedback: After the PCB prototype is completed, the problem should be reported to the relevant personnel

A. Feedback to the person in charge of the biotechnology model of the problem points of PCB model boarding for review and improvement;

B. Collect the PCB prototype problems found in the trial investment in the factory, and feedback to the person in charge of PCB prototype printing;

C. Feedback the improvement of the trial investment problem to the person in charge of the PCB prototype;

D. Track the improvement of problem points.

Precautions during the first mass production stage of PCB model making:

Second, the precautions for the production of the first mass production stage of the PCB prototype

It refers to the models that have been mass-produced after trial production and improvement. Some models are trial-commissioned and mass-produced at the same time. Generally, the batch size is more than 100. In the same production, you need to pay attention to the following:

1. Preparation of PCB model board:

A. Understand production arrangements with purchasers;

B. Preparation of patch data (schematic diagram, patch map, bom table, FW, driver, burning tool)

C. Understand the basic functions of the model, formulate test procedures and test items;

D. Understand the post-welding components of PCBA, formulate the post-welding process (try to prepare sop), and clarify the precautions for post-welding;

E. Master the method of burning FW for the model;

F. Formulate the process requirements and production precautions of the entire PCBA;

G. Clarify the condition of the test fixture, make sure that the test fixture is OK, try to find a sample for test;

H. Understand the accessories and equipment required for testing, special equipment needs to be proposed in advance, and test accessories are prepared in advance;

I. Prepare a model;

2. Confirmation of materials and data:

A. First understand the situation of material preparation, whether the material is complete will determine the production arrangement, and if the material is not complete, it should be reported to the factory immediately;

B. Confirmation of key materials, such as the version and material number of major materials such as FWIC, BGA, PCB board, etc.; material confirmation must check the BOM;

C. The general manufacturer's IQC and material staff will also check the materials. If there are any inconsistent materials, they should immediately check with the development engineer;

D. Materials that have changed after the trial investment;

3. First article confirmation:

A. Confirm the first piece of the patch, pay attention to the direction and specifications of the main components, check the first piece record of the PCB model maker, and check the model at the same time;

B. After the furnace, the PCB needs to look at the tin consumption of each component and understand the furnace temperature curve (can be retained);

C. Instruct the first post welding operation, confirm that all post welding components are correct, and must meet the process requirements, and check the SOP of the corresponding post welding station;

D. Follow the test process to guide the test function test to ensure that all the main functions of the PCB are tested;

4. Analysis and confirmation of defective products:

A. Understand the straight-through rate of the test, confirm the main adverse phenomena and causes and record them;

B, the problem of PCB template boarding operation is immediately forwarded feedback, requiring immediate control of the front section;

C. Because of material problems, feedback immediately to confirm whether it can be produced and how to produce, it is best to take photos and keep files;

5. Information feedback:

A, feedback the problem points in the production of PCB prototypes to the person in charge of the biotechnology model to remind them;

B. Collect the assembly problem points in the factory, feedback to the person in charge, and request improvement;

Precautions for production in the mass production stage of PCB model making:

Third, the production precautions in the mass production stage of PCB model making

A certain model has been mass-produced many times by the same manufacturer, and the process and flow are relatively familiar. In some cases, the following matters should be paid attention to:

1. Confirmation of test fixtures: Confirm the conditions of test fixtures and test accessories before production; collection of previous problem points;

2. Special material confirmation: confirm the abnormal materials before production, and confirm the materials in one field;

3. First article confirmation:

A, make a simple understanding and test of the first article, and check the relevant first article record;

B, check whether the previous problem occurred again and whether the hand was improved;

C, confirm whether the previous process and process need to be improved;

4. Analysis and confirmation of defective products;

Make a simple analysis of the defective products, understand the main defective distribution and the main causes, and try to improve it;

5. Information feedback

A, feedback the problem points in the production of PCB prototypes to the person in charge of the biotechnology model to remind them;

Collection of assembly problem points in factory B, feedback to the person in charge, and request for improvement;

The development trend of PCB prototype electronic components:

With the further improvement of mobile consumer electronic products for miniaturization, functional integration and large storage space requirements, there are more and more miniaturized high-density packaging forms of components, such as multi-module packaging (MCM), system packaging (SiP) ), flip chip and other applications are becoming more and more. The emergence of component stacking assembly (PoP, Package on Package) technology has further blurred the boundary between first-level packaging and second-level assembly. While greatly improving the logic operation function and storage space, it also provides end users with free choice of device combinations. Possibly, production costs can also be controlled more effectively.

Needless to say, with the advent of miniaturized high-density packaging, the requirements for high-speed and high-precision assembly have become more critical. Related assembly equipment and processes are also more advanced and highly flexible.