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Pcb technology puts several schemes of SMD on FPC

Author:Luwis zeng Date:9/1/2018 10:13:55 AM
 According to the accuracy requirements of placement and the types and quantities of components, the commonly used schemes are as follows: scheme 1, multi-chip placement: multi-chip FPC is positioned on the carrier half by positioning template, and is fixed on the pallet together with SMT Placement.

1. Scope of application: A, component type: chip components generally have a volume greater than 0603, and QFQ and other components with a pin pitch greater than or equal to 0.65.

B. Number of components: several components to more than a dozen components per FPC.

C. Mounting accuracy: The placement accuracy is medium.

D, FPC characteristics: the area is slightly larger, there are no components in the appropriate area, each FPC has two MARK marks for optical positioning and two or more positioning holes.

2. FPC fixing: According to the CAD data of the metal leakage plate, read the internal positioning data of the FPC to manufacture a high-precision FPC positioning template. The diameter of the positioning pin on the template is matched with the diameter of the positioning hole on the FPC, and the height is about 2.5 mm. There are two lower pins on the FPC positioning template. A batch of pallets is made based on the same CAD data. The thickness of the pallet is about 2mm, and the warpage deformation of the material after several thermal shocks is small, and the good FR-4 material and other high-quality materials are preferred. Before performing SMT, the pallet is placed on the pallet positioning pin on the template so that the positioning pin is exposed through the hole in the pallet. Place the FPC one by one on the exposed fixed pin, fix it on the pallet with thin high temperature resistant tape, do not let the FPC offset, then separate the pallet from the FPC positioning template, carry out welding printing and placement, and withstand high temperature. The adhesive tape of the tape (PA protective film) should be moderate, and must be easily peeled off after impact at high temperature. Moreover, there is no residual glue on the FPC.

It is important to note that the shorter the storage time between the start of the FPC and the placement of the FPC on the pallet, the better.

Solution 2: High-precision placement: Fix one or several FPCs on a high-precision positioning plate for SMT mounting 1. Scope: A, component type: almost all conventional components, QFP with pin pitch less than 0.65mm also may.

B, the number of components: dozens of components or more.

C. Mounting accuracy: In comparison, QFP mounting accuracy with a high placement accuracy of 0.5mm pitch is also guaranteed.

D, FPC characteristics: large area, there are several positioning holes, MARK mark with FPC optical positioning and optical positioning mark of important components such as QFP.

2. FPC fixing: FPC is fixed on the component pallet. This positioning pallet is mass-customized, with high precision and high precision. The difference in positioning between each pallet is negligible. This type of pallet has a small dimensional change and warpage deformation after a high temperature impact of several decades. The positioning plate has two positioning pins, one of which has the same height as the FPC, and the diameter matches the aperture of the positioning small hole of the FPC. The other T-shaped positioning pin is slightly higher than the former. One point, because the FPC is very flexible, large in size, and irregular in shape, the role of the T-shaped locating pin is to limit the offset of certain parts of the FPC, ensuring printing and placement accuracy. For this fixing method, the place corresponding to the T-shaped positioning pin on the metal plate can be appropriately treated.

The FPC is fixed on the positioning plate, although the storage time is not limited, but due to environmental conditions, the time should not be too long. Otherwise, the FPC is prone to moisture, which causes warping deformation and affects the quality of the placement.

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