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How to optimize PCBA manufacturability through device package optimization design

Posted by: Yoyokuo 2022-10-19 Comments Off on How to optimize PCBA manufacturability through device package optimization design

With the rapid development of modern Electronic technology, PCBA is also developing towards high density and high reliability. Although the current level of PCB and PCBA manufacturing processes has been greatly improved, the conventional PCB solder mask process will not have a fatal impact on product manufacturability. However, for devices with very small device pin spacing, due to the unreasonable design of PCB flux pads and PCB solder mask pads, it will increase the difficulty of SMT welding process and increase the quality risk of PCBA surface mount processing.In view of the hidden problems of manufacturability and reliability caused by the unreasonable design of PCB flux and solder mask pads, combined with the actual process level of PCB and PCBA, it can be optimized through device packaging.

With the rapid development of modern electronic technology, PCBA is also developing towards high density and high reliability. Although the current level of PCB and PCBA manufacturing processes has been greatly improved, the conventional PCB solder mask process will not have a fatal impact on product manufacturability. However, for devices with very small device pin spacing, due to the unreasonable design of PCB flux pads and PCB solder mask pads, it will increase the difficulty of SMT welding process and increase the quality risk of PCBA surface mount processing. In view of the hidden problems of manufacturability and reliability caused by the unreasonable design of PCB flux and solder mask pads, combined with the actual process level of PCB and PCBA, the manufacturability problem can be avoided by optimizing the design of device packaging. The optimization design mainly starts from two aspects, one is the optimized design of PCB LAYOUT; the other is the optimized design of PCB engineering.

Current Situation of PCB Solder Mask Design

PCB LAYOUT Design

The package design is based on the IPC 7351 standard package library and the recommended pad size in the device specification. In order to design quickly, Layout engineers give priority to increase and modify the design according to the recommended pad size. The length and width of the PCB soldering pads are increased by 0.1mm, and the solder mask pads are also different in length and width on the basis of the soldering pads. Increase by 0.1mm. As shown in Figure 1:

How to optimize PCBA manufacturability through device package optimization design

(Picture 1)

PCB Engineering Design

The conventional PCB solder mask process requires that the edge of the soldering pad be covered by 0.05mm, and the solder mask bridge between the two soldering pads should be larger than 0.1mm, as shown in Figure 2 (2). In the PCB engineering design stage, when the solder mask pad size cannot be optimized and the solder mask bridge between the two pads is less than 0.1mm, the PCB project adopts the group pad window design process. As shown in Figure 2 (3):

How to optimize PCBA manufacturability through device package optimization design

(Figure II)

PCB solder mask design requirements

PCB LAYOUT Design Requirements

When the edge distance between the two flux pads is greater than 0.2mm or more, the package should be designed according to the conventional pads; when the edge distance between the two flux pads is less than 0.2mm, DFM optimization design is required. Optimization design methods include solder flux and solder mask pad size optimization. Ensure that the solder mask process solder resist can form a minimum solder mask bridge isolation pad when the PCB is fabricated. As shown in Figure 3:

How to optimize PCBA manufacturability through device package optimization design

(Figure 3)

PCB engineering design requirements

When the edge distance between the two flux pads is greater than 0.2mm or more, the engineering design shall be carried out according to the conventional requirements; when the edge distance between the two pads is less than 0.2mm, DFM design is required. The engineering design DFM method includes the optimization of solder mask design. And the soldering layer copper cutting treatment; the copper cutting size must refer to the device specification, the soldering layer pad after copper cutting should be within the size range of the recommended pad design, and the PCB solder mask design should be a single-pad window design , that is, the solder mask bridge can be covered between the pads. It is ensured that during the PCBA manufacturing process, there is a solder mask bridge between the two pads for isolation, so as to avoid the appearance quality problems of soldering and the reliability of electrical performance.

PCBA process capability requirements

Solder mask can effectively prevent solder bridges from short-circuiting during the soldering and assembly process. For PCBs with high-density fine-pitch pins, if there is no solder bridge between the pins for isolation, the PCBA factory cannot guarantee the local soldering quality of the product. For PCBs with high-density fine-pitch pins for isolation without resistance soldering, the current processing method of the PCBA manufacturing factory is to judge that the PCB material is not good, and it will not be produced online. If the customer insists on going online, in order to avoid quality risks, the PCBA manufacturing factory will not guarantee the welding quality of the products. It is foreseen that the welding quality problems that occur during the manufacturing process of the PCBA factory will be dealt with through consultation.

case analysis

Device data sheet size

As shown in Figure 4 below, the device pin center spacing: 0.65mm, the pin width: 0.2 ~ 0.4mm, the pin length: 0.3 ~ 0.5mm.

How to optimize PCBA manufacturability through device package optimization design

(Picture 4)

PCB LAYOUT actual design

As shown in Figure 5 below, the size of the soldering pad is 0.8*0.5mm, the size of the soldering pad is 0.9*0.6mm, the center distance between the device pads is 0.65mm, the distance between the soldering edges is 0.15mm, and the soldering edge is 0.15mm. The spacing is 0.05mm, and the width of the unilateral solder mask is increased by 0.05mm.

How to optimize PCBA manufacturability through device package optimization design

(Figure 5)

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