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PCB Requirements for Typical SMT Equipment

by: Nov 22,2018 76 Views 0 Comments Posted in PCB Assembly

SMT

Introduction:

There are many types of SMT equipment. How to make the design of PCB meet its requirements is decided by the type of equipment. The basic requirements of typical SMT equipment to PCB in China are summarized as follows.

Edge (Break-away tab):

PCB in the process of SMT equipment is generally completed by rail transportation. When locating in equipment such as patch machine and wave soldering, it is guaranteed that it can be fixed reliably. Generally, more than 5mm should be reserved at the side of transport track to allow the track to be held. If the reservation cannot be made, it should be added, about 5mm process edge. As shown in figure 1:

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If the PCB design is not a rectangle, consider adding a “Break-away tab” so that it has two parallel sides. Otherwise, corresponding clamps should be made in production to ensure that PCB can adapt to SMT equipment, so that PCB can be positioned in the SMT machine and transmitted in other SMT equipment, as shown in figure 2.

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Toaling Hole:

Part of the printing press and the patch machine use the positioning pin when positioning the PCB, which requires that the positioning hole should be reserved when making the PCB. Different devices may have different requirements for locating holes. Generally, a pair of locating holes should be arranged at both ends of the rectangular PCB, and the aperture is usually 4mm, /span> the two holes are in the lower left and lower right corner of the PCB. If the SMT equipment is transmitted from right to left, the left hole center position should be 5mm from both sides of the PCB, the right hole center position is 5mm from the bottom of the PCB, and there is no requirement to the distance on the right. But the two holes should be on both sides of the center of gravity of the PCB to support the PCB, as shown in figure 3. From left to right, the opposite is true.

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Note: Do not attach any component within 3 mm around the toaling holes.

Products with PCB function need to be tested by the online testing equipment. There should also be a pair of toaling holes in the diagonal of the PCB, and the aperture and spacing requirements should be determined according to the testing equipment. The non-rectangular PCB is made by referring to the rectangular PCB adding break-away tab.

Baseline:

In order to correct the positioning error, warping and distortion of PCB during mounting, most SMT equipment uses optical reference positioning. Baseline is done with regular geometric shapes, and the dots or round holes which the diameter is usually 0.8mm or 1.5mm are generally preferred. The baseline can be used for PCB full-board baseline, fine spacing devices, component level baseline for BGA and CSP components, and the block baseline for the daughter boards of the mother boards.

Generally, 2 reference points are required as a group, and a 1 mm diameter dot or round hole is preferred. The board-level baseline shall be arranged in a set of diagonal of the PCB, and the positions of the two reference points should be arranged as far as possible until the rectangle formed by their diagonals can envelop all the SMT components. Similarly, component and block baselines are similarly distributed diagonally. See figure 4.

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When the baseline point is a dot (highlight), a soldering zone, which no soldering pads and wires shall be required in this zone, shall be set aside and shall be 1.5mm larger than that. When the baseline point is a round hole (dark point), a ring, required to cross tin and be flat and shiny, shall be set aside and shall be 1.5mm larger than that. The tin plating part of the baseline point should be irradiated by the optical system and have high contrast with the surrounding area after the hot air rectification and equal surface treatment, which is conducive to the recognition of the baseline point. The tin plating part of the baseline points will have a high contrast with the surrounding area when it is detected by the automatic optical detection system after the hot air rectification and equal surface treatment, which is conducive to the recognition of the baseline point.

PCB Identification and Output Data:

In order to facilitate the processing, or the demand of EMS, the following identification and output data are required when the PCB design is transferred to the production and processing department after completion:

(1) The name of the PCB, the position and polarity of components, PCB marks and production date, etc.

(2) Material list, the PCB drawing, the template file making, the patch programming file and other prescriptive documents. If the test is needed, the schematic diagram and network table are required.

(3) Test conditions, standards, quality testing standards and specifications of the products after soldering.

(4) Other requirements of EMS.

Conclusion:

The standardized design of PCB is beneficial to the standardization construction of enterprises, and it can effectively guarantee the reliability, scale and production of products, which plays a due role in reducing cost, improving efficiency and guaranteeing product quality. They should be taken seriously by businesses, and so should SMT practitioners.




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