Printed circuit board

SMT placement process flow design

SMT is surface assembly technology, is a new generation of electronic assembly technology developed from hybrid integrated circuit technology. SMT is widely used to promote the miniaturization and multi-functionalization of electronic products, and provides conditions for mass production and low defect rate production. SMT processing process involves many aspects, and the specific requirements are as follows.

SMT namely surface assembly technology, is a new generation of electronic assembly technology, from the development of hybrid integrated circuit technology. SMT mounting technology is widely used, greatly promote the miniaturization of electronic products, multi-functional. And SMT placement process design many aspects of the process, there are many specific requirements, today, let’s take a look at it.

A, PCB and IC baking

1. PCB is not more than three months, and no moisture phenomenon, no baking. More than 3 months after the baking time of 4 hours
2. Temperature: 80-100 degrees; IC: BGA package
3. 1 month after the bulk, to bake 24 hours, the new bulk package to bake at least 8 hours, if the old or disassembly material IC to bake 3 days temperature: 100-110 degrees; QFP/SOP/other package IC original vacuum packaging does not need to bake, bulk at least 8 hours, temperature: 100-110 degrees

Second, SMD

1. Solder paste process
2. Red glue process
3. Leaded process
4. Lead-free process

Third, the type, model, nominal value and polarity of each assembly bit number components and other features marked

To conform to the product assembly diagram and the detailed list or BOM requirements (should be burned into the IC whether or not to carry on the burning record), mount the good components to be intact.

Fourth, mount components solder end or pin not less than 1/2 thickness to be immersed in solder paste.

For the general components SMD when the amount of solder paste extrusion (length) should be less than 0.2mm, for narrow pitch components SMD when the amount of solder paste extrusion (length) should be less than 0.1mm.

Fifth, the end of the components or pins are aligned with the pad graphics, centered.

Due to the reflow soldering process of self-positioning effect, the installation position of the components allow certain deviations. Allowable deviation range requirements are as follows.

1. Momentary components: in the direction of the width of the component weld end width of more than 1/2 in the pad; in the direction of the length of the component weld end and the pad must be overlapped; when there is a rotation deviation, the component weld end width of more than 1/2 must be in the pad.
2, small form factor transistor (SOT): X, Y, T (rotation angle) deviation is allowed, but the pins (including toe and heel) must all be in the pad.
3, small form factor integrated circuit (SOIC): allow X, Y, T (rotation angle) have placement deviation, but must ensure that the device pin width 3/4 (including toe and heel) in the pad.
4、Quadrilateral flat package device and ultra-small package device (QFP): To ensure that 3/4 of the pin width is on the pad, and allow X, Y, T (rotation angle) to have a small placement deviation. Allow the toe of the pin to stick out of the pad in a small amount, but there must be 3/4 of the pin length on the pad, the heel of the pin must also be on the pad.

Sixth, the conventional SMD material must comply with IPC-310, IPC-610 standard.

Seven, the board surface must be clean

There must be no tin beads or dross visible to the blood eye.

Eight, test range

Check whether the light is on, whether the searcher is searching for IP, test whether the image is normal, whether the motor is rotating, test the voice, test the voice monitoring and intercom, the machine and the computer should sound.

Nine, sampling test

The above is the SMT processing process of each step need to follow the requirements of Oh, Jie DuoBang in SMT chip processing has been strictly follow such a requirement process, each step to the highest standard requirements for themselves, and strive to provide the best quality service.


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