PCB Technical - PCB process OSP surface treatment PCB production process requirements

PCB process OSP surface treatment PCB production process requirements

1. OSP PCB production requirements

1. The incoming PCB material should be vacuum packed, with desiccant and humidity display card attached. When transporting and storing, use separator paper between PCBs with OSP to prevent friction from damaging the surface of OSP.

2. Do not expose to direct sunlight. Keep a good warehouse storage environment. Relative humidity: 30～70%, temperature: 15～30 degree Celsius, shelf life is less than 6 months.

3. When unpacking at the SMT site, you must check the vacuum packaging, desiccant, humidity display card, etc., and the unqualified boards are returned to the manufacturer for rework and reuse, and go online within 8 hours. Do not disassemble multiple packages at once, follow the principle of dismantling and producing, and producing as much as you dismantle. Otherwise, the exposure time is too long and it is easy to cause poor quality welding in batches.

4. Go through the furnace as soon as possible after printing and do not stay (the longest stay is no more than 1 hour), because the flux in the solder paste is very corrosive to the OSP film.

5. Maintain a good workshop environment: relative humidity 40～60%, temperature: 18～27 degree Celsius.

6. During the production process, avoid touching the PCB surface directly with your hands to prevent the surface from being contaminated by sweat and oxidized.
7. After the SMT single-sided patch is completed, the second-sided SMT component patch assembly must be completed within 12 hours.
8. After completing SMT, complete the DIP plug-in in the shortest possible time (up to 24 hours).
9. Moisture OSP PCBs cannot be baked. High-temperature baking can easily cause discoloration and deterioration of OSP.

10. Overdue empty boards, damp empty boards, and empty boards cleaned after poor printing in batches that have not been used in production should be returned to the circuit board manufacturer for OSP rework for re-use, but the same board cannot be reworked more than three times, otherwise it will need to be scrapped. .

2. OSP PCB's SMT solder paste steel mesh design requirements

1. Because OSP is flat, it is beneficial to solder paste forming, and PAD cannot provide part of the solder, so the opening should be appropriately enlarged to ensure that the solder can cover the entire pad. When the PCB is changed from spray tin to OSP, the steel mesh is required to be reopened.

2. After the opening is appropriately enlarged, in order to solve the problem of tin beads, tombstones and OSP PCB exposed copper in SMT CHIP parts, the opening design of the solder paste printing stencil can be changed to a concave design, and special attention should be paid to anti-tin beads.

3. If the parts are not placed on the PCB for some reason, the solder paste should also cover the pads as much as possible.

4. In order to prevent the exposed copper foil from oxidizing and causing reliability problems, it is necessary to consider printing ICT test points, mounting screw holes, and exposed through holes with tin paste on the front side (wave soldering on the reverse side), and full consideration when making steel mesh Make a hole.

Three, OSP PCB printing solder paste poor board processing requirements

1. Try to avoid printing errors, because cleaning will damage the OSP protective layer.

2. When the PCB printing solder paste is not good, because the OSP protective film is easily corroded by organic solvents, all OSP PCBs cannot be soaked or cleaned with high volatile solvents. You can wipe the solder paste with a non-woven cloth dipped in 75% alcohol and use an air gun Blow dry in time. Do not use isopropyl alcohol (IPA) for cleaning, and must not use a stirring knife to scrape off the solder paste on the poorly printed board.

3. After the PCB is cleaned with poor printing, the SMT patch soldering operation on the heavy industry PCB surface should be completed within 1 hour.
4. If there is poor printing in batches (such as 20PCS and above), it can be handled in a centralized way to return to the factory for heavy industry.

Four, OSP PCB reflow oven temperature curve setting requirements

The setting requirements of the reflow soldering temperature curve of OSP PCB are basically the same as that of the tin-sprayed board, and the maximum peak temperature can be appropriately lowered by 2-5°C.

5. Notes:

1. OSP process introduction: OSP is the abbreviation of Organic Solderability Preservatives, and the Chinese meaning is: organic protective film, also known as copper protective agent. It is to coat a layer of OSP film (usually controlled at 0.2-0.5um) on the (double-sided/multi-layer/two-layer) bare copper pad for protection, replacing the original process of spraying tin on the surface of the pad. technology. The advantages of OSP PCB: PCB production cost is low, the surface of the pad is flat, and it meets the requirements of lead-free process.
Disadvantages of OSP PCB: high requirements for use (limited time use after opening, time limit completion of the front and back, plug-in wave soldering production), high storage environment requirements, PCB surface is easy to oxidize, usually cannot be baked and reused if damp, and poorly printed boards cannot be cleaned casually Reuse etc.