With the rapid advancement of electronic technology, miniaturization, BGA packages, and high-density chips with pitches as small as 0.3mm to 0.5mm are becoming increasingly common. As a result, the demands on soldering techniques have never been higher. While automated placement machines have largely replaced manual soldering in many cases, numerous factors still influence the quality of the final solder joints. This article aims to highlight key considerations during PCB design from the perspective of surface mount technology (SMT). By following these guidelines, you can significantly reduce the risk of poor soldering, bridging, or even damage during rework.
**I. Factors Affecting PCB Soldering Quality**
Achieving high-quality solder joints requires strict control at every stage—from PCB design to component placement and soldering. Key factors include the PCB layout, board quality, component quality, pin oxidation, solder paste quality, printing accuracy, placement machine precision, assembly quality, and the reflow oven temperature profile. Among these, the PCB design itself is one of the most critical elements that the manufacturing team cannot easily compensate for.
Many PCB designers lack hands-on soldering experience, which means they may not fully understand how their design choices impact the soldering process. On the other hand, factory workers often don’t have a deep understanding of the design, leading to potential issues that go unnoticed until it's too late. Bridging these knowledge gaps is essential for ensuring consistent and reliable soldering outcomes.
**II. Recommendations for PCB Design**
Below are several practical recommendations for PCB designers to improve soldering quality and avoid common pitfalls:
1. **Positioning Holes**: Place four positioning holes (minimum diameter 2.5mm) at the corners of the PCB for accurate solder paste printing. The center of the X-axis and Y-axis should align precisely.
2. **Mark Points**: Use clear and distinct mark points for the placement machine to identify the board’s position. These should be placed diagonally, either as round or square pads, and not mixed with component pads. If the board has components on both sides, mark both sides.
3. **Clearance Around the Edges**: Ensure at least 3mm of space along the long edge of the PCB for the placement machine to handle the board without interference. Avoid placing components within this area.
4. **Avoid Vias on Pads**: Placing vias directly on component pads can lead to solder paste flowing into the via, resulting in insufficient solder at the pad and potential weak joints.
5. **Polarity Marking**: Clearly indicate the polarity of diodes and tantalum capacitors to prevent incorrect orientation during soldering.
6. **Silkscreen Clarity**: Avoid cluttering the silkscreen with unnecessary text, especially on densely populated boards. Keep labels simple and readable for both human operators and automated systems.
7. **Extended IC Pads**: For packages like SOP, PLCC, and QFP, extend the pads to allow easier manual soldering. The pad length should be about 1.5 times the length of the IC pin.
8. **Pad Width**: Ensure the width of the PCB pads matches the IC foot dimensions. Avoid widening the pads to prevent bridging between adjacent pins.
9. **Component Orientation**: Do not rotate components at arbitrary angles. Placement machines typically only support 90°, 180°, or 270° rotations. Misalignment can cause misregistration and poor solder joints.
10. **Shorting Adjacent Pins**: Avoid using shorting traces that are hard to distinguish after soldering. Instead, use solder masks or separate the connections clearly.
11. **Center Pad Considerations**: For chips with a central pad, reduce its size to increase spacing from surrounding pads and minimize the risk of shorts.
12. **Device Spacing**: Avoid placing high-profile components too close together. This can cause mechanical interference during the second pass of the placement machine.
13. **BGA Considerations**: For BGA packages, add two 30-mil locating holes on the PCB for easier stencil alignment during rework. Also, leave some space around the BGA for proper solder paste application.
14. **PCB Color**: Avoid red PCBs, as they can appear white under the camera light used by placement machines, making them difficult to detect.
15. **Small Components Under Large Ones**: Avoid placing small components beneath large ones, as this complicates rework and risks damaging the larger component.
16. **Copper Pad Connections**: Avoid connecting pads directly to large copper areas, as this can cause uneven heating and lead to cold solder joints. Isolate the pads from large copper regions if possible.
17. **Process Edges**: Consider adding process edges to the PCB for better handling during manufacturing, especially when space is limited.
**III. Conclusion**
Today, many engineers are skilled in designing and routing PCBs using advanced software, but it's equally important to consider the practical implications of those designs on the soldering process. By paying attention to the above points and developing good design habits, you can greatly enhance the reliability and efficiency of your PCB manufacturing. Always communicate effectively with the production team and think ahead—every engineer should take responsibility for the entire lifecycle of the design.
Water Heater Breaker
Leakage protector, also known as leakage switch, is a new type of electrical safety device, mainly used for:
(1) Prevent electric shock accidents caused by electrical equipment and electrical circuit leakage;
(2) Preventing single-phase electric shock accidents during electricity use
(3) Timely cut off single-phase grounding faults in the operation of electrical equipment to prevent fire accidents caused by leakage
(4) With the improvement of people's living standards and the continuous increase of household appliances, personal electric shock and fire accidents caused by defects, improper use, and inadequate safety measures of electrical equipment in the process of using electricity have brought undue damage to people's lives and property. The emergence of leakage protectors provides reliable and effective technical means for preventing various accidents, timely cutting off power, and protecting equipment and personal safety.
The leakage protector should meet the following technical requirements
(1) The sensitivity of electric shock protection should be correct and reasonable, and the starting current should generally be within the range of 15-30 milliamperes
(2) The action time of electric shock protection should generally not exceed 0.1 seconds
(3) The protector should be equipped with necessary monitoring equipment to prevent it from losing its protective effect when the operating state changes. For example, for voltage type electric shock protectors, a neutral grounding device should be installed.
ZHEJIANG QIANNA ELECTRIC CO.,LTD , https://www.traner-elec.com