SMT production line process
Operation Preparation: SMT production line of all workstations personnel standardized wear anti-static bracelets, work shoes, overalls, work hats
SMT production line process:
(1) static-sensitive components, humidity-sensitive components, based on the "ESD Protection Management Program", "moisture-sensitive components management program," stored and record.
(2) each bottle of solder paste labeled "solder paste labeling sheet" stored in the refrigerator, once a day to check the temperature in the refrigerator (0 ~ 10 ℃)
printing solder paste:
(1) solder paste
(a) warming: from the refrigerator to take out the smallest number of the solder paste (first-in, first-out principle), fill in the warming time, take out the beginning time, two hours later for the end of the time. time. Put back in the temperature box, room temperature natural warming for two hours.
(b) Stirring: When the rewarming time is over, put the solder paste into the blender and stir for 2 minutes.
(c) Use:
①.IPQC confirms that the rewarming time is qualified before operation.
②. The service life is 24 hours after opening. If it is not used, store it in the bottle with the cap closed and refrigerate it.
3. If the stencil paste is not used for more than 30 minutes, store it in the bottle and close it.
④. Environmental requirements: Temperature 22～28℃, humidity 45～65%.
(2) stencil:
(a) Tension measurement: each time before the use of the measurement of the tension value of the five positions and record, less than 30N/cm? When the person in charge of timely notification processing. Based on the "stencil control role approach".
(b) Cleaning:
①. Before/after use, use dust-free wiping paper, propanolol to clean the stencil surface and the bottom layer, air gun blowing off the mesh foreign matter.
②. In the printing process, every ten printed circuit boards or printing quality defects, immediately cleaning.
③. According to the "stencil cleaning methods", "printing quality inspection standards"
(3) Semi-automatic printing machine debugging:
(a) Assembly: Confirm that the circuit board in line with the order of the type of machine → Fixed circuit board in the printing machine workstation → stencil openings aligned with the circuit board pads after locking → Qigong stencil to move down and complete the fit with the circuit board, tighten the adjustable turntable.
(b) Paste volume adjustment:
①. Pour paste on the steel net, manually control the scraper back and forth evenly paste, gradually increase the amount of paste, cover all the pads of the circuit board, and scraper ends of the paste overflow.
②. Scraper scraping, stencil surface if the residual paste, adjust the pressure of the scraper to scrape the residual paste.
(c) solder paste thickness confirmation:
①. Paste thickness gauge to measure the thickness of the paste in five areas of the circuit board.
②. Thickness standard: lower limit = stencil thickness minus 0.01mm, upper limit = stencil thickness plus 0.045mm.
③. According to the "solder paste thickness gauge operation standard book"
(d) printing quality inspection: the operator checks each piece of processed products, if there is a burr, even tin, less tin, leakage of printing phenomenon, timely cleaning of the mesh, increase the amount of solder paste on the stencil.
Mounting machine placement:
(1) program documents to confirm:
(a) according to the order of the type of machine to retrieve the corresponding placement program.
(b) Load the board, confirm the MARK point, patch position, if there is offset, adjust the XY coordinates.
(2) Confirmation of feeder material:
(a) According to the engineering BOM table, each specification and size of the tape material, corresponding to the installation of the feeder.
(b) According to the content of the patch program, install the feeder in the designated station number.
(c) Confirm the material programmed by each feeder in turn, if the feeding is incorrect, unstable, or shifted, adjust the feeder and adjust the XY coordinates of the head suction nozzle.
(3) after the patch check / debugging:
(a) start the patch machine automatically paste a circuit board, whether there is offset, side flip, leakage / multiple pieces, reverse polarity, wrong pieces of bad phenomena.
(b) bad cause correspondence:
①. Offset: the clamping track is too wide, the circuit board origin offset, bad nozzle, patch coordinates offset.
②. Side flip: feeder feed instability / jitter, bad nozzle.
③. Leakage / multiple parts: patch program error, bad nozzle, insufficient air pressure.
④. Reverse polarity: Feeder is loaded with the opposite material, wrong patch program.
⑤. Wrong parts: wrong feeder loading, wrong patch program.
(c) Appearance inspection after placement: After the first piece of self-inspection, notify the IPQC to check and confirm and tell them to pass before they are allowed to work.
Reflow soldering:
(1) Documentation confirmation:
a. According to the order type of machine to retrieve the corresponding machine documents.
b. Confirmation of parameter settings: heating zone temperature, chain speed, fan frequency.
(2) Confirmation of soldering effect:
a. Put three pieces of pasted boards into reflow soldering.
b. Under the magnifying glass (40 times) to check all the welding position, whether there is a tin bead, cold welding, even tin, standing monument, false welding bad phenomenon, whether the solder joints are bright, the reaction of the residue, the pad wetting is not enough.
c. Corresponding to the causes of defects:
①. Tin beads: preheating zone heating rate is fast, short constant temperature time in the constant temperature zone, poor solder paste printing, poor solder paste characteristics.
②. Cold soldering: long preheating zone, low temperature in the soldering zone, short soldering time in the soldering zone, poor solder paste characteristics.
3. Continuous tin: preheating zone heating rate is fast, paste printing offset bad, SMD components offset.
④. LIBERTY: low temperature in the preheating zone, short constant temperature time in the constant temperature zone, uneven thickness of solder paste printing, offset of SMD components.
⑤. False soldering: constant temperature zone constant temperature time is long, pad / component metal layer pollution oxidation, pin deformation warping, solder paste amount of small / thin.
6. Solder joints gray without luster: welding area welding time is long, the cooling area cooling rate is slow.
⑦. More residue: low temperature in the preheating zone, low temperature in the welding zone; black residue: high temperature in the welding zone, long time in the constant temperature/welding zone.
⑧. Insufficient wetting: high temperature in the preheating zone, low temperature in the constant temperature zone, poor solder paste printing offset, pad contamination oxidized solderability.
d. Reflow soldering temperature profile requirements: (based on the temperature profile of the solder paste manual to set the parameters, KIC pyrometer to measure the furnace temperature, once every two weeks.)
Preheating zone: temperature range → room temperature ~ 150 ℃, time → 60 ~ 90 seconds, the optimal heating slope → 1 ~ 3 ℃ / sec
Constant temperature zone: temperature range → 150 ~ 217 ℃, time → 60 ~ 120 seconds
Soldering zone: temperature range → 217 ~ 245 ℃, time → 20 ~ 50 seconds
Cooling zone: Temperature range → 217 ~ 150 ℃, the optimal cooling slope → 2.5 ~ 6 ℃ / sec
(3) three circuit board welding effect of self-checking qualified, notify the IPQC check to confirm and inform the qualified before operation.
After the furnace appearance check:
(1) Chip IC materials using electronic magnifying glass under visual inspection to confirm.
(2) According to the order machine type to call the corresponding AOI inspection program.
(3) AOI inspection operation:
a. The operator verifies and confirms the defective objects detected by AOI.
b. Confirmation of defective products, attached to the red label, isolated to the defective products box, and recorded in the report.
c. If there are three consecutive occurrences of the same defective object, immediately notify the person in charge to deal with it.
d. Confirmation of qualified products, placed in the anti-static swing frame.
e.According to the "After Oven Appearance Inspection Work Standard Book"
Maintenance of defective products: according to the red labeling, maintenance of defective products, and record the treatment measures in the report of repair.