English (UK) 
简体中文 You just took over the SMT workshop production line management, is not always found on the speed chain transmission of the circuit board somehow damaged? Obviously, the accuracy of the mounter is not a problem, but always in the transmission chain out of trouble? Do not panic! This is eighty percent of the static electricity in the dark rubbing ghosts. Today we will break open the crumbs to talk about--How a novice can quickly master the multiplier chain antistatic, on these five life-saving points!
I. Grounding system: do not let static electricity "hold" in the chain
This thing is clattering all day long, and if the static electricity generated by friction has no place to run, it can "electrify" the precision chip in a minute. It is crucial to build a "floodway" for it:
- Independent grounding is an iron rule! The equipment grounding wire must be separated from the power supply grounding, and the grounding resistanceMust be less than 10Ω, which is equivalent to building an exclusive motorway for static electricity.
- 1MΩ resistor cannot be omittedThe "safety valve" must be strung between the chain and the grounding wire! Between the chain and the grounding wire must be strung this "safety valve", in case of 220V leakage, the current can be suppressed to less than 5mA (people touch will only numb a little bit, will not be electrocuted).
- Don't mess around with the location.The more contact area you have, the faster the static electricity runs off! Copper plate grounding effect far away from the copper rod a few streets, the larger the contact area of static electricity run faster.
I've seen too many factories hitch the multiplier chain directly to the device housing - end of story! This is the equivalent of dumping static electricity back into the machine and the chip dies easier than stepping on an ant.
Second, the choice of materials: the chain itself must be "static electricity nemesis".
Plastic rollers from a normal speed chain? That's a walking "static generator"! The real solution is:
- Surface resistance value jammed 105-108Ω-cmThe material (for example, conductive rubber mixed with carbon black), static electricity comes and immediately leads away without residue.
- Metal parts must be anodisedBare metal conducts electricity too quickly! Bare metal conducts electricity too quickly, discharges like lightning splits the chip, and adds a layer of oxide film to the surface for a soft landing.
- Comparison table to understand the gap in seconds::
| Material type | surface resistance | Static dissipation rate | risk level |
|---|---|---|---|
| Plain PVC Roller | >1012Ω-cm | lit. as slow as a snail's pace | ⚡⚡⚡⚡⚡ |
| Carbon black compound rubber | 106-108Ω-cm | Zero in 1 second | ⚡ |
| Anodised aluminium alloys | 105-107Ω-cm | 0.5 second drain | ⚡ |
(Data consolidated from)
Third, environmental control: humidity dropped to 30%? hurry to open humidification!
The drying room is a carnival party for static electricity!Humidity 45%-70%RHIt's a dead line, below 30%? Wait for the chip carcass to be collected! Hands-on focus:
- Ultrasonic Humidifier Works Better Than Splashing WaterThe water is chlorinated and corrodes the circuits! Tap water contains chlorine that corrodes circuits, you have to use a water purification plant.
- Don't hang the thermo-hygrometer on the wall.! Put one at the head and one at the tail of the production line, and immediately adjust the air conditioner when the temperature difference exceeds 3℃.
- cold knowledge: When you heat 5C air to 20C in winter, the humidity will plummet from 65% to 24%! So you have to humidify before heating.
Fourth, personnel protection: the operator is the "mobile electrostatic bomb"
A person can take two steps and carry 5000V static electricity, touching down the speed chain the whole line is finished! We have to tie up the "human electric baton":
- Anti-static wristbands should be worn against the flesh! Sleeves on the equivalent of nothing, direct skin contact in order to conduct away static electricity.
- Chain of custody is insurance.: Anti-static shoes + conductive floor mats + grounded wrist strap, the three-piece set is indispensable.
- lesson learnt through blood and tears: A factory employee wearing chemical fibre underwear to work, cuff friction generates 12kV static electricity, passing through the multiplier chain directly through the whole batch of PCB - so uniforms must also be all-cotton!
Fifth, equipment maintenance: monthly not to do this 3 equal to do nothing!
Antistatic systems are not a one-off solution!Monthly Must-Do List::
- Wristband tester dislikes: Resistance value not in the 1-10MΩ range? Change it immediately!
- Megohmmeter to measure chain resistance: Roller surface resistance exceeds 108 Ω. Alcohol scrub or replace with new one.
- Ionisation fan calibration: The static voltage at 50cm from the air outlet must be 0±50V, and the tungsten needle should be replaced if the deviation is large.
Self-questioning time!
Q: Why is there still static electricity damage in the sampling test even though the protection is done according to the specification?
A: 80% of them are planted inconcealed locationOn! For example, the doubler chain bracket is sprayed with insulating paint, or the earth wire is wrapped in oil - take a multimeter and focus on the chain link articulation and the ground stake!
I've been doing SMT for ten years, I've seen too many factories to spend money on high-end mounter, but can't afford to change the speed chain for an anti-static guide. Remember ah.Static damage to a chip is never "quantity to quality."-Today the electricity does not die, tomorrow becomes inferior, the day after tomorrow the customer directly returned! These five strokes implemented, at least to keep your 99% yield.
