how not to hurm the SMD  ?  - Page 1
Forum section: electronics / beginners

author: eevblogfan
author_rank: Frequent Contributor
timestamp: June 15, 2012, 09:08:31 am
content: SMD soldering :well , I've manegd to get 5Xmcp6V27 ,do I need antistatic math ?here's a little "thinkering" :will it be safe to solder on it ?ther's a bit of dust on the pink metirial and on the shilded sheet either , is it assential to clean it ?is it ok to just wind abit of alominum foil around my right hand and connect it to my HP's earth binding post ? (the shilded sheet as well )thank you in advance and have anice day !

author: T4P
author_rank: Super Contributor
timestamp: June 15, 2012, 10:39:54 am
content: Using a al foil will most certainly1) When it gets in contact with the chip, and your static goes to it, all bets are off2) Very very bad idea3) Usually a little bit of dust doesn't matter, when it has quite a lot you know for certain the chips inside are okay if there isn't any insideThe dust outside is alright, but lots of dust can signify anti static bag failure

author: LEECH666
author_rank: Frequent Contributor
timestamp: June 15, 2012, 10:48:06 am
content: I'd say: Unless you're very serious about what you're doing don't bother. If you are, get a real ESD matt plus wristband. You will need to move those SMD parts to the PCB at some point anyway, with no antistatic plastics between the board and the chip at all, so why bother with soldering them on the plastic bags? The platic bag will probably just melt.Florian

author: eevblogfan
author_rank: Frequent Contributor
timestamp: June 15, 2012, 12:42:34 pm
content: welltoo lateI've lost my patience !and the op amp is well well with in spec ! ( compare to my very bets 2 meters -> 287 and 3478A ) ]I dont have the need for that matt , when I will I'll buy one like dave has ( to protect the workbench as well )I grownded myself and the shilded sheet , and I dont think I've maneged to hurm the chip , I dont have any SMD to throo hole adapter , so I took 8 pin shoket and I've solderd 1 hair of 20AWG wier to each pin , ohh that was furstrating !!! BUT it was well worth it !

author: A Hellene
author_rank: Frequent Contributor
timestamp: June 15, 2012, 12:52:46 pm
content: Readthis thread, please.In short, do never let the ESD sensitive devices be in the electrical path of any electrostatic discharge.Additionally, an ESD mat might not be an absolute necessity; but anantistatic wrist strapis:Antistatic wrist strap-George

author: LEECH666
author_rank: Frequent Contributor
timestamp: June 15, 2012, 01:02:59 pm
content: I don't use an ESD matt myself, however my soldering irons are ESD "safe".I've have yet to fry a device with electrostatic discharge. *knocks on wood*I don't handle a lot of sensible parts tho.OT: Just wondering if all these typos are some sort of slang, or unintentional. @eevblogfan

author: eevblogfan
author_rank: Frequent Contributor
timestamp: June 15, 2012, 02:00:41 pm
content: funnyI'm 16 years old , english is not my main language , hence I use to write as correct as I can , though , I don't have alot of time to correct any single word ,well , I did "wrist straped " myself , alominum foil connected to 18AWG wier with bana plug direct to the earth binding post of the HP-3610A , I know my poor soldering iron is not ESD safe , but at least he's tip is earthed ,the ofset between the fluke 287 and the HP-3478A ( both recently cale'd ) is about 10uV ,if the 287 claim 2.346mVthe HP-3478A claim 2.356mV , the 1uV resolution is somehow constantly within spec ,

author: A Hellene
author_rank: Frequent Contributor
timestamp: June 15, 2012, 02:04:26 pm
content: Hehe! I can remember (with a subtle smile on my face) grounding myself by using a crocodile clip (with a 100 kohm in-series resistor) attached to my watch's metallic bracelet while learning/playing/working at my home bench, during my gymnasium and high-school years in the late seventies/early eighties!I will proudly state that I have never harmed a component or a device by ESD. But I cannot say the same for damages I have done (and I still occasionally do!) by placing the components in wrong polarity or by applying the wrong voltages, due to my hastiness and my overly self-confidence...My theory is that people learn by their own mistakes, the smart ones learn by the mistakes of the others, and the hopeless people do never learn!-George

author: free_electron
author_rank: Super Contributor
timestamp: June 15, 2012, 02:20:40 pm
content: Ouch, ai, ow, oei... So many halfunderstood things about ESD In one post.....Time for a little lesson, gather around, grab a comfortable chair, slippers, sigar, glas of brandy and stok up the fireplace... Time for a long story....First of all: what is static electricity , and what sets it apart from 'regular' electricity?Well, regular electricity is the flow of electric charge, carried by electrons, in a conductor. A conductor is a material that has plenty of electrons that are willing and capable of traveling.Static electricity is exactly the opposite. It is an accumulation of electrons that are unable to move. For some external reason, they were piled up in a certain spot and they are trapped there. They cant move because they are stored on the surface of an isolator.Voltage is determined by how many electrons you pack in a certain area. In a conducting material the voltage differential between, lets say 10 atoms, next to each other is tiny. Because the electrons on the outer shell will move and charge disperses. In an isolator it can be large since the electrons cant move or disperse. So here you can build a large charge.I mentioned 'external' reason. Well, something must pile the electrons in a heap. They are not going to do this for fun, or by themselves, since they are pretty much immobile ( immobile in the sense of hopping from atom to atom. They still do circle ).The external reason is the movement of two materials in respect to each other. Friction! But, not just any friction or materials. We need two different materials. Rubbing two sheets of the same plastic together does not create static charge. We need a material that is a really good isolator, and a material that easily traps electrons. When the surfaces meet, the material that easily traps electrons will pick off electrons from the other material and transport them across the surface of the other material. When contact is broken this leaves the electron pattern disturbed. You will have areas with few electrons and areas with many electrons. All on the same material.Now, remeber, the electrons are trapped. So by themselves this is not doing anything ! The charge simply sits there, immobile.Now things become interesting, but before that a litle sidetrack.Lets do a little experiment. Take a roll of cellotape. The well known 3m brand 'invisible' tape. , take a firm hold of the end of the roll and pull out a length of a good 2 feet of tape as fast as you can. Take care to hold only the end of the tape. The tape reel should be in a holder on the table ( holding the roll in your hand creates a conductive path through you and negates the effect somewhat... ) or being held by someone else who is well isolated from you.Let go of the end of the tape. The stretch of tape will curl up in on itself and become a sticky, untangible, mess of tape you can only throw away.What just happened here ? Well, this is static electricity at play... An adhesive is a material that easily bonds itself to other materials. At a molecular level adhesive works by sharing and grabbing electrons from other atoms. The plastic foil in the tape is treated in such a way that one side can grab the adhesive really well, the other side to a lesser extent. ( without treatment the adhesive would peel off, off the tape and just remain wherever it felt like. The surface treatment makes sure the adhesive remains firmly on one side and lets loose of the other side so you can neatly unroll it.)By rapidly pulling out a stretch of tape we created friction. The adhesive was able to steal a bunch of electrons while it was pulled away from the underlying material. The non adhesive side has lost a bunch of electrons. So we created a charge differential ( a 'potential'). Like charges repel, dislike charges attract. Because adhesive works by sharing electrons it is very good at stealing a lot of them. That little strip of tape you pulled out can hold as much as 10 kilovolts... The strip of tape is effectiveley a capacitor. The adhesive is one plate, charged with electrons, the non adhesive side is void of electrons.... The barrier between them the dielectricum.So, if you let go , the charges start repelling and aatracting, and because the material is so light, actually manage to move the stuff around and have it curl up in a sticky mass.Now, back to the interesting bit and the consequences.We have a charge differential , a 'potential'. Charge can be removed by creating a conductive path... Like a piece of metal. Potential, or 'voltage' through a conductor creates a current. The ple of electrons moves. The bigger the pile ( the voltage ) and the wider the path ( the wider path is lower resistance ) the bigger the flow is going to be. The flow is electrons per second or... Ampere !Basis of ohms law.So if you take a piece of copper wire and you short out the static charge : no harm done.But take a very tiny piece of wire and you get another problem... The voltages we play with are large. The resistance of the wire may be pretty high.. Current through a resistor creates loss in terms of heat. P = V x I. And V is very large. So even for moderate R ( giving small I ) P is large.Take the guts of a transistor which is made, today, in submicron... And things get nasty.. Very quickly.If the potential is high enough, electrons will skip over small isolation barriers as well. Small isolation barriers such as found inside modern transistors and chips...So you have two effects : because structures are so small and the potential so high the discharge does two thing: it creates so much heat it vaporises the electrical connections in the chip... And the elctrons skip over the tiny isolation barriers to aggregate inside the chip and when enough charge is present there they also fry adjacent parts in the chip.... It is a cascade effect.... The vaporising metal creates shorts elsewhere and gives the charge new pathways to cause more and more damage. This goes on until the charge is enough dispersed that the remaining voltage levels are not high enough to further push the electrons around.So here is the key: static charge in itself is not dangerous, provided you do NOT let it move! Once you give it a pathway disaster strikes!If you have two electrical components, charge to the same potential, you let them touch each other, no electrons will flow, no harm will be done. Have two components at different potentials that meet and there will be a current to balance the charge. This current can be destructive! If potential difference is high enough the current will be sufficient to cause damage.More in a bit..let take another sidetrack here. What is a 'spark' a spark is an electrical current flowing through a 'resistance' dissipating enough power so it creates enough heat to light up and start combustion. Combustion is a chemical process whereby elements bind with each other giving off heat and photons. Is a spark fire ? Debatable (especially by specific religious groups) . Fire creates enough heat , and has enough fuel to keep the process going. Take away the fuel or decrease the heat and the fire dies. In a spark the energy source if voltage... collapse the voltage, the current drops , power dissipation drops , temperature drops, reaction stops...So a temporary spark is just a very short lived fire.. if you have a constant arc going on ( like welding ) then you are feeding fuel ( current and materials to burn )Same with lightning. Air is a pretty poor conductor, but make the voltage potential large enough and you will make a spark . lightning will ionise the air ( it will pull up electrons through better conducting area's like where there is a lot of water droplets in the air ) a 'feeler' of ionized elements will create a weak conuctive path after which the main discharge just lets it rip... the temperatures reached are so high that even oxygen oxidizes ( now chemists and fysiscits no doubt raise an eyebrow ) but in short that is what happen. an oxygen molecule (O2) binds with a single oxygen atom (O) to form O3 , or .. ozone. If temeprature is high enough crazy things happen... ozone is not stable and will fall apart pretty quickly.anyway, enough sidetracking.in short :Static charge , or voltage , succeeds in letting a current run through a conductive path. A conductive path has resistance. Current through a resistor creates power dissipation. power dissipation is heat . Heat vaporises the small structures in chips. The vaporized metal condenses ( cools down) and creates new pathways for the current to do more damage ( if there is energy left ). if the voltage is large enough it can skip even better 'resistances' and do more damage.even shorter :high voltage = baddamage done because of current.So, what can we do to eliminate the problem?Well , we can restrict the current... by injecting resistances of our own. If there is a charge this will limit the current to safe zones and no harm will be done.Enter the conductive ESD material. mainly carbon based and in the order of 100K to 10 Meg. everyone knows the black esd foam. That is there to create a resistive pathway and let charges level out gracefully.But that is a a post-cause remedy... the cause is the high potential.. we should not let that build in the first place !We need to make sure these charges cannot develop in the first place.get rid of perfect isolators for example. your workbench should have an ESD mat. preferrably a doublesidedone. top layer dissipative material ( 200 meg to 500 meg ) so tat charges cannot accumulate fast enough. they will disperse. backed by a conductive (black carbon ) to wick away the dispersed charge to a common reference point.Now, here is a myth that needs busting. 'everything should be grounded'. This is wrong. The real rule is 'everything should be at the same potential'. In other words: there should be no potential difference. Potential difference creates current . creates heat .. you know the drill by now...So why 'ground'. Well, because of these stupid bipedal lifeforms that have a need to use their ambidextrous 5 digit protrusions to manipulate things.. like picking them up and putting them somewhere else. You got it. us humans are the source of the problem.since we walk on a surface, and we are slightly conductive it makes sense to refere everything to the potential of that surface. If i am sitting on the floor.. that is my 'ground'. if my lab is a metal box hanging from a 100 kilovolt power line then the 100 kilovolt line is my ground. as long as everything inside my lab is also at 100 kilovolt ( 100 kilovolt for the outside observer ) there is no problem. It is potential: voltage difference. everything inside the metal box is at the same potential. if i need to hand something from inside my lab to someone standing outside , that sits at a different potential than my lab ... we're looking at a potetntial darwin award ....So, unless you are an evil scientist that has a lab floating from a 100kv line.. you will be at the potential of planet earth. Simply called earth potential.( simple logic innit ? potential of planet earth = earth potential )so ,we refer everything to this reference plane. how ? by creating conductive paths. But , we need to restrict current.. so we use megaohms reistors.Wristraps , esd mats, chairs , esd clothing, soldering tips .. anytihng that is conductive needs the flow of current restricted using a resistance , and , connected to a common reference point : earth reference.the resistnce needs to be there to restrict current. not only to avoid large currents from frying chips and transistors , but also from preventing us humans from frying... apply sufficient voltage so you can send roughly 50 millliampere through a human so the heart muscle cramps up , blood flow stops and its brain dies because of oxygen starvation and you end up with a dead human...so : some of the WRONG thing i read in this postLet's use aluminium foil : WRONG ! this is waaaay too good of a conductor if you have a chip body charged and you touch the aluminum you may cause a discharge. only one pin is going to touch first ! you can't guarantee all pins touching exactly the same... aluminun foil s a good shield to PREVENT charge buildup , it is bad if you already have a charge ...i find it amusing that people take a pice of styrofoam , put an aluminum sheet on top and poke the parts in there.. styrofoam is a tremendous charge accumulator...aluminum a really good conductor. See the trouble brewing ?And then they toss multiple of these sheets on top of each other... yikes !strapping yourself to aluminum directly to ground is extremely dangerous to you. touch a live wire and you will die !you need a 1 meg resistance to protect yourself ( screw the chip in this case. there's plenty more in the factory... only one 'you' ) Having a 'grounded' soldering tip is equally bad. it should connect through a 1 meg resistor ! and you need a grounded power outlet too... or else it does nothing.'an esd mat is not necessary ..ehh if your bench i a really good isoator and is charged in respect to the part you drop on it.. it will fry it ! your bench needs to be at same potential and you need to prevent charge buildup. there are cleaning products like 'staticide' that make a bench dissipative. but there stillneeds to be a pathway to the common reference.te 'thinkering bit : you got the order wrong....here is a bit of info on those ESD bags.There are 3 kinds of bags. Dissipative, conductive and anti-static.An anti-static material is a material that will not build up a charge when friction is applied. yuo can rub it with whatever you want , you cannot push electrons around. these are the pinkish bags and bubble wrap. Most of this material works because it is also dissipative (but not necessary) dissipative means youcan push electrons in heaps but there is enough conductivty to self balance. anti-static menas : you can't push them in lumps to begin witha conductive bag is used for shielding. this is the grey silver metallic bags. these have a problem.. the conductive element is a vapor deposited metal foil between two sheets of dissipative material.. in itself no problem. but, if you have a board with sharp ins , or batteries , and the pins poke through the bag : disaster... i have seen LiThiocl cells explode because the battery pins poked through such bags...A board must be wrapped in dissipative material to protect it. and then stored in a conductive bag to shield it from the outside.a dissipative bag by itself is not enough protection. if the voltage potential is high enough it cannot dissipate quickly enough across the bag. current will seek the path of the least resistance.. and that may be your part !have a component with its pins poke through a dissipative bag and zap one pin with an ESD gun and you will kill the component !the pink bag is there so the friction of theboard on the bag does not create charge, and to provide mechanical dampening ( in case of the pink bubble wrap )the metallic bag is there to shiled the whole thing from outside zaps.if you open packaging from digikey you will find parts in light blue colored bags , inside metallic bags. The light blue bags are dissipative and will not accumulate charge and disperse whatever there is on the chip.The metallic bag prevents zapping.There is another thing : ionizing radiation. this can cause static charges as well. the metallic bags shield that, the pink stuff don't. parts that travel by airplane are subject to higher doses of radiation ( both on the ground in the x-ray machines ) and in the air where they are exposed to cosmic radiation ( cargo planes are less shielded than passenger planes... ). Anything that goes in an airplane needs a metallic bag around it !And then you have the cross-hatched bags. This is dissative material impregnated with a lattice of conductive pathways. Ideal for circuitboards: no risk of shorting batteries and better shielding against zaps than dissipative bags alone.Now, al this stuff only works if it is all referenced to a common potential. simply stacking it on top of each other and then poking the part with a charged soldering tip is still a recipy for disaster.you donlt need a billion dollar ot make an ESD safe workplace. get some 1 megaohm 1 watt resistors ( or better take three 330k resistors of 1/4 watt and solder them in series ) and connect the tip of the soldering iron through this resistor to the gournd of the power bar. buy an esd mat and a wriststrap and off you go. make sure to always put tools and bags first on the mat before you grab inside the bag to pull a board out...the reason for the 1 watt resistor or three resistors is to protect us humans... resistors have a voltage rating. a 1/4 watt resistor can flash over ... a 1 watt resistor has a lnger body that will not flash over that eaily. three 1/4 watt resistors have an even longer body.

author: gtyrrell1
author_rank: Contributor
timestamp: June 15, 2012, 08:31:54 pm
content: free_electronJust curios, I am new to this whole thing. i get the anti static mat, but the resistor thing...not really sure what that looks like. I am pretty much a beginner and long term am looking at doing component level chip replacement on logic boards.(I am an Apple guy). I currently own a computer repair company and so far we send out any damaged boards to repair shops. I am hoping eventually to do these repairs in house so as to save on time and costs.Also, where can I purchase the materials to make an appropriate work bench. What materials would you recommend?ThanksGilbert

author: T4P
author_rank: Super Contributor
timestamp: June 15, 2012, 09:02:23 pm
content: Quote from: gtyrrell1 on June 15, 2012, 08:31:54 pmMaterials? Who cares if it's wood or plastic!A double sided ESD mat is black on the bottom and usually another colour on the topHere's my top gray colour ( Definitely beyond 220Megohms, manual says 1Gohm max but certainly not anywhere near 220megohms )

author: M. András
author_rank: Super Contributor
timestamp: June 16, 2012, 09:46:58 pm
content: wondering about which pin is the ground point on the weller ground plug im too lazy to check it out

author: Mint.
author_rank: Frequent Contributor
timestamp: June 16, 2012, 11:08:29 pm
content: Hey free_electron,Awesome little article thereYou've certainly cleared up some things for me and probably anyone else who didn't know much about ESD. Thanks!

author: free_electron
author_rank: Super Contributor
timestamp: June 17, 2012, 02:12:32 am
content: Quote from: M. András on June 16, 2012, 09:46:58 pmTurn the spldering iron on and then sit on it, the part that burns you posterior is the grounded part

author: Rerouter
author_rank: Super Contributor
timestamp: June 17, 2012, 02:31:17 am
content: thank you free_electron, your story, lesson, large post? contained a few things i wasnt aware of,

author: free_electron
author_rank: Super Contributor
timestamp: June 17, 2012, 03:53:58 am
content: Oh, there's plenty more... Like how to protect a circuit board from getting zapped inside a box...After all the board will be used at a certain point and will leave the bag to end up inside a product. It will need protection there too....Esd zaps can screw up working equipment and make it go wonky or even reboot it.Well designed equipment will use a barrier ring at the circumference of a board. A strip, about half a centimeter to a centimeter wide where soldermask is removed. This ring is connected to the screw holes. The ring exists top and bottom layer and has plenty of via's shot into it to make it low impedant. The ring is not directly comnected to the circuits ground. It is directly connected to chassis ground.The connection between the ground of the circuit and chassi ground goes through a couple of ferrite beads and a few caps. The caps need to be 2 kilovolt class . Esd discharges are very narrow pulses and a ferrite bead will sufficiently block these as it forms alarge impedance for such a fast rise time.So the energy will not get blasted into the circuit ground but disperse into chassis ground ( path of least resistance ). For dc signals the ferrite bead is , for all purposes, 0 ohms so good electrical ground is maintained.Any opening in a non-conductive box where a connector protrudes should have such a guard ring. If a discharge creeps through the opening it will strike the bare area first .A moat of about 5 mm should be kept between guard ring and other parts. The moat is only half covered in soldermask. So 5 mm copper , 2.5 mm bare pcb , 2.5 mm covered pcb ( no copper under soldermask ) thenthe rest of the board.Chassis chiseld like the outside of a usb connector, ethernet connector db9 db 25 ps2 and others should be connected to the guard ring. The ground pin of the connector is connected to the normal plane.A ferrite bead / cap combination should be placed close to every connector. If all connectors are lumped together like on a pc motherboard you can get away with a pair left and right of the lump.When i was making the adsl modems for alcatel this was one of the tests it underwent. An esd gun was used to zap close to any vent hole and seam on the plastic enclosure. Having the guard protected the system perfectly. No crashes at all.At the same time you can use the guard ring to mitigate emc problems as well... Any internal emc shielding should be connected only to the real ground and not to chassi ground.If the plastic box has a metal film sputtered on it this can be connected to the guarding ring.The guard ring is the part connected to the earth lead in a mains cable.For a system connected only by usb the connection is through the shield on the usb cable.Low voltage dc powered systems connect through the outside earth wire.If you look at power supply bricks for laptops these use a coax type cable. The outer braid is a shield that connects to earth. The center conductor feeds the circuit. In this case you need to connect the guard ring and the system ground through a common mode choke. Any zap will get injected into the power brick cable and will not get into your electronics. There are special common mode filter blocks with built in capacitor for this purpose. They are 4 wire elements.System ground , system power to the inside system and guard ground + power in that comes from the power brick.The fat ground wire from the power brick goes to guard ground. The common mode filter transfers the dirty ground to the system ground. Any zap in the guard , or the cable is effectively stopped.There's more.... Just ask. I sometimes don't recall everything unless a specific question is asked.

author: eevblogfan
author_rank: Frequent Contributor
timestamp: June 17, 2012, 07:02:01 am
content: WoW !thank you free_electron !that's one hell of invested post(s) , you've reveal few points I'll use further to my job .have a nice day

author: bingo600
author_rank: Super Contributor
timestamp: June 17, 2012, 07:18:43 am
content: This is probably the best ESD post i have ever read , and i think i'll get an antistatic mat nowThanx for making this subject understandable to "Non professionals"My Quick 202 soldering station has 1Meg from the tip to GND , and a banana jack 2-Ohms to GND.I guess thats were my mat and wristband should be connected , after i have checked that they have 1Meg in their current path (wire).Most mains outlets here in DK , doesn't have GND.But i have recently changed all my powerstrips to ones with GND , so at lest all my instruments has same GND potential).But after i read this i'll now get the GND from my powerstrips connected to the metal of my (radiator / heeating pipe) in my working room.As i read it "Effective ESD killing" , the ESD also need a path to "Get away".Like via the pipe .... (The house we live in is "older" ... meaning no plastic/PVC pipes yet ....)/Bingo

author: Unknown
author_rank: Unknown
timestamp: June 17, 2012, 09:56:49 am
content: Quote from: bingo600 on June 17, 2012, 07:18:43 amPlease read free_electron's extensive explanations more care carefully:Quote from: free_electron on June 15, 2012, 02:20:40 pmConnecting your wrist strap to your local ground would bring you to the same potential, even without connection to physical earth. Connecting the local ground to PE would have nothing to do with the 'ESD getting away', there is no magic to go earth potential that makes all electrons want to go there. Please don't think of radiator pipes as safety ground, and keep in mind that equipment with a grounded plug is designed to be used with a proper safety ground connection to be safe in the case of a single fault.

author: M. András
author_rank: Super Contributor
timestamp: June 17, 2012, 11:37:10 am
content: Quote from: free_electron on June 17, 2012, 02:12:32 ami laughed a good on your postit was funny.btw i went up to the attic to get the earth plug for the wd1m, it its plugged in only the center pin has connection to the iron. if its removed there is a approx 200kohms resistance to the mains earth pin and to the rest of the station

author: G7PSK
author_rank: Super Contributor
timestamp: June 18, 2012, 02:31:14 pm
content: And don't forget if you and everything around is at earth potential and there happens to be a static charge on your board when you pick it up components can still get zapped which is another reason you need the current limiting resistor in the ground circuit.