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What You Should Know Before Repairing PCB

Printed circuit boards are widely regarded as the main component of the majority of electronic devices used on a daily basis. Mobile phones, no matter how small, televisions with large screens, and all other devices make use of printed circuit boards. As an electrical engineer, there is a great chance that you will be dealing with printed circuit boards every day. This may be needed for your new device or just updating for an already existing track or circuit.

PCBs can become damaged for different reasons. At times, this printed circuit board could become damaged beyond any repair; however, other times, these damages are repairable. PCBs are known to be an important component, the reason why repairing them perfectly is very important. A bad pcb repair could lead to electrical short circuits

Furthermore, ensure that your circuit board repair is handled by a professional. There are some people that prefer learning how to repair printed circuit boards, here we are to help.

What are the First Steps to Take During Printed Circuit Board Repair?

PCB repairs could be very challenging. To repair circuit board, it is important that you have the necessary skills and knowledge regarding the subject. Let us quickly consider ways by which you can perform circuit board repair.

Identify what the problem is

The very first thing you should do during printed circuit board repair is to identify the problem by diagnosing it. What part of the PCB is causing the issue? Once you are able to identify this malfunctioning part, and then see it you will be able to replace it using a different but similar component. You may also need to get the same part.

You can replace some pcb components using a similar component. Note however that any defective part playing a unique function must be replaced using a similar component.

You must choose a setting

Note that printed circuit boards feature many small components. Therefore, to repair this circuit board, you must be extremely vigilant. Get the necessary tools for the repair. However, before you start anything, ensure that you are using the right platform.

You may either tape your circuit board to your table or use some clippers to hold it as you work. Remember to trim excess tape because this prevents the movement of the circuit as you work. Asides from this, there is a need to have the necessary accessories and tools ready on your desk.

Get rid of the defective or failed component

Use a hot air gun to get rid of the failed component from your printed circuit board. As soon as you turn on the hot air gun, hold it some inches above that part that is defected. This helps in loosening that defective component. After that, you can now pull it out using tweezers.

Soldering of the PCB Components

Get some copper braids of a special length and then place them onto the PCB pad. Put them in one place from where this defective component has been removed from. After placing this copper braid on your pad, make use of the soldering iron tip and then apply as little heat on your copper braid.

These copper braids aid in absorbing the additional solder on your PCB pad. As soon as you have completed this step, make use of clean alcohol swabs in cleaning these pads. Don’t make use of wet clothes and other cloth materials. The best possible option when you need to clean printed circuit board pads are alcohol swabs.

Join this new and perfectly working component on PCB Pads

Now, the next thing to do in PCB repair is connecting these new components to the PCB pads. This part is very significant and you need to take serious caution and care when performing this. Here are two important things that you must consider when joining this new component onto the pad.

First, is the component’s orientation and positioning. You have to place it in a specific position like the old component. If you change the orientation and position of these new components, this may cause a short circuit in the printed circuit board. Furthermore, the PCB will fail to function if you don’t perform the connections correctly.

Also, make use of soldering iron and solder in connecting the components leads with the links present on the pad. The pad or trace needs this.

What are the Safest Ways of Handling Printed Circuit Boards During Repair?

You need to take serious care when you are handling PCBs. This is to ensure that more damage doesn’t come during the repair. Below are some of the issues you need to worry about.

Discharge and unplug your electronics

In order to avoid your electronics from experiencing short circuits and possibly causing electrocution, ensure that you unplug the faulty device and discharge it completely. Power supplies and capacitors can hold charges. This is why you have to pay much attention to ensure that they are totally discharged. Also, if there are supplemental batteries, make sure you disengage them too.

Put on safety glasses

Safety glasses are very important because the solder could splatter and leads could fly during trimming. Therefore, make sure you put on safety glasses. This offers some protection for your eyes during pcb repairs.

Prevent any static discharge

ESDElectrostatic discharge involves the quick flow of some electrons, or a spark that occurs between surfaces. This is due to a differential formed in-between these surfaces, with one possessing more electrons compared to the other.

Furthermore, nature really loves equilibrium; therefore, there is an exchange of electrons in order to equalize this distribution. When you wear a wrist strap that is grounded and working on an ESD-safe mat, also grounded is a very reliable way of preventing ESD. The wrist strap features a conductive surface, which touches the skin, therefore making it possible for the bleeding off of excess electrons.

ESD-safe mats function using a similar principle, therefore bleeding off charges from its surface. Also, if you are using a PC, the wrist strap can be directly clipped to the case’s unpainted area directly.

Wash your hand and handle just the edges of the Printed Circuit Board to Reduce possible contamination

Contamination from the hands can lead to solderability issues. It can also result in board failure as a result of dendritic growth or corrosion. Silicon from your usual hand lotion or you picked it up mistakenly from somewhere could form a barrier on the contact areas, which could prevent this solder from creating a strong metallurgic bond.

Furthermore, this solder might stick temporarily, but at exposure to physical or thermal stress, it may pop off. Contamination, such as salt on fries you consumed with lunch is another cause of issues that come in during the repair. Salt is ionic and when it combines with moisture present in the air could cause corrosion. These ionic particles could also join and form dendrites leading to leakage and short circuiting.

Also, wash your hands making use of hand lotions that are electronic safe only. This is a way of preventing this board failure type. Furthermore, holding only the edges of the board without contacts could help in preventing the deposition of contaminants on the critical areas.

How to Fix Soldering Mistakes

Soldering has to do with the combination of two metal surfaces making use of solder, flux, and hot soldering iron. Removing this solder when something goes wrong becomes more complicated.

You may need to replace or remove bad components or excess solder. Below are the common methods for solder removal. You can also call this desoldering.

Solder wick

This is also called wick or desoldering wick, which refers to copper braids which are useful in absorbing solder. Generally, it is coated using flux, to ensure that melted solder is drawn up and also retained combining both capillary and wetting action.

With a solder wick, you will be able to remove solder present in the isolated areas without causing thermal stress to the circuit board or its nearby components. With a solder wick, you can only remove my exposed solder, there components that are covering the contact areas such as BGAs must be taken out before you can remove the residual solder.

Solder suckers

This makes use of a vacuum, which draws up the melted solder.  You need to melt the solder either using hot air or soldering iron, like from a rework station or a heat gun. You can only draw up small quantities of solder at a time. It may also take many attempts to get rid of a component. When you remelt the solder joint or you maintain the soldering temperature, it leads to increase of thermal stress on the other solder joints, the components, and the circuit board.

With solder suckers, you can only remove the exposed solder. Therefore components that are covering the contact areas such as the BGAs (Ball Grid Arrays) must be removed before you can remove the residual solder.

Desoldering stations

These feature a soldering tip with a hole present in the center, which draws up all the solder immediately after melting. While this is very effective, the rework station only has the ability to get rid of exposed solder, so that components that are covering the contact areas such as the ball grid arrays must be removed before you can remove the residual solder.

Hot air solder stations

The hot air solder stations help in blowing hot areas over that repair area. This helps in melting the solder. Using either a vacuum lifter or tweezers, you can remove the component. Once you have removed the components, you have to find another way to remove the solder.

Hot tweezers

The idea here is clamping to the leads present on the component’s sides in order to melt the solder all at once. With this, you are limiting the thermal stress in contrast to hot air. Immediately you have removed the components, then you have to find another way to remove the solder.

Hot plate

When you place the PCB on reflows or hot plate melts on the solder joints, it will allow you to get rid of different components all at once. Using this method may cause stress for other components as well as the board.

Tips to Ensure High Quality and Efficient Desoldering

Ensure the soldering iron tip is tinned and clean for better heat conduction

This is usually overlooked and it is important for better and efficient desoldering. When oxidation and burnt flux covers the soldering iron tips, it won’t get wet, therefore leading to poor heat conduction.

A tinned and clean soldering tip helps in conducting heat better via the desoldering braid and also begins the wicking faster.

Reducing the Time that the Board and its Components Stays at High Temperature

When you apply high heat to the components of the board, or the board itself for long time periods, this can cause some damage to the board and its components. It can also create solder joints that are brittle, which can cause service issues.

Match the Width of the Wick to the Contact Pad or Solder joint

Generally, desoldering wick come in different widths. Therefore, the braid can be matched to whatever you’re desoldering. Too thin wick will not get rid of enough solder and will need toy to remelt and trim the solder repeatedly. Too wide wick will take a longer time to heat. Also, it may affect other printed circuit board components.

Match the Tip of the Soldering Iron to the Braid Width in Order to Ensure Accuracy

Make use of soldering tip that has a similar width to the contact area and braid. Too small tip will need more dwell time. Also, too large tip can expose the other components, especially when the assembly is dense.

When you match the size of the tip, it allows the melting of any unwanted solder quicker. It also reduces the time for heat application. Make use of a knife tip or blade during the desoldering of large areas such as BGA pads.

Match the Flux Type to the Cleaning Process

There is desoldering braid in different flux types. This depends on the cleaning process, as well as other requirements. The quickest wicking action is called the Rosin fluxed braid. However, this leaves back residues which you have to clean thoroughly. When cleaning isn’t possible or practical, it is advisable to use a no-clean fluxed braid.

When you are done desoldering, one thing stays clean, which is the non-ionic residue. Also, when serious or thorough cleaning becomes more challenging like during field work, then you should use this braid type.

Protect the Board against Possible Corrosion by Making Use of a Top-quality Flux Remover

Printed circuit board assemblies can exercise corrosion and dendritic growth due to flux residues. This is why you must make use of the best practices when cleaning the circuit board. After replacing all the components, and you have removed excess solder, you have to clean that area properly using a top-quality flux remover.

How to Get Rid of Conformal Coating During PCB Repair

The best technique or method for getting rid of coating has to do with the coating type, as well as the components’ sensitivity.

Urethane (UR)/ Silicone (SR) / Acrylic Coatings

During desoldering, you can burn through urethane, silicone, and acrylic coatings. This can cause rough or burned edges, which you will need to clean up before you recoat. You can remove these coatings chemically, making use of either common solvents or specialized solvents such as acetone, Xylene, or toluene. These are all very harsh. Xylene and toluene have toxicity problems. Therefore, ensure that you put on appropriate PPE. Also, make sure that there is enough ventilation.

Parylene (XY) / Epoxy Resin (ER)

Parylene and epoxy coatings are tough coatings, which are resistant to chemical and physical stresses. These are the properties, which makes then very effective and making the removal difficult. You cannot use chemicals to strip the resins.

It may be possible to melt or burn them off. However, there is a risk – the circuit boards may get damaged. Micro-abrasive method is the best and most acceptable when removing Parylene and epoxy coatings.

For micro-abrasive blasting, it makes use of a special device in blowing the abrasive particles all over this coated surface. Also, you will need to choose the abrasive medium with extreme care, to ensure that the process doesn’t bring any damage to the rest of the surface, markings, or components. Also, the repair area has to be masked. This isolates any blasting effect.

Ultra-Thin Coating

This is becoming a very common method for all consumer electronics such as mobile phones. You cannot view it with the naked eyes and it scrapes away and burns easily.

How to Patch Your Conformal Coating After PCB Repair

It is advisable that you use a similar coating material like the initial PCB assembly. You should specify this in the device’s service manual. In the electronic repair world, you may not know what was initially applied. For this case, coating making use of acrylic coating is the easiest and best solution.

Overcoat pens are acrylic conformal coatings which are present in convenient packaging. You can make use of the clear version to coat the small areas. Just press the pen tip down and then squeeze that barrel so as to release that coating material. Furthermore, for areas that are larger, you can apply conformal coating making use of an acid brush.

No matter the way you coat, ensure that you prevent coating connectors. The coating should be done around them. You can also mask them with a temporary solder mask, or Kapton tape. Don’t use the adhesive copper tape; this is because this copper tape melts quickly.

Repairing a Broken Trace on a Printed circuit board

A well-known method of repairing a broken trace is by soldering on a jumper. This is a wire bypass formed around this broken trace. The process is both visually unappealing and time consuming.

You can use conductive pens. This is made up of very conductive material such as nickel or silver that is suspended into a liquid polymer. With these pens, you will be able to redraw this trace.

Below are steps to take to effectively and quickly repair a broken trace using the conducting pen.

  • You will need to expose some of the surface area of the initial trace to ensure great electrical continuity. If a solder resist exists right to the break, you can utilize a sharp blade in breaking away a part of the resist, say 1/16.
  • Clean that area using either a swab that has been saturated using solvent cleaners such as isopropyl alcohol.
  • Shake your conductive pen vigorously till you hear the rattling of the internal ball
  • Press the break area of the pen tip, then squeeze up the pen barrel so as to dispense off the conductive ink.
  • Wait for one hour at least, for the conductive ink to cure before you go ahead to repair the overcoat.

What are the Other Repairs for PCBs?

Gold Finger Repair

These are the features present on the PCB’s periphery. Here, they are usually subjected to solder splash when wave soldering is on. If you discover that the edge contacts have become contaminated either with solder or otherwise, then the printed circuit board may fail to work the way you want it.

Through-Holes

Through holes as well as eyelets are important for multilayer boards to function properly. The through holes have the ability to sustain damage due to improper removal of the part or rough handling. Due to this damage, the printed circuit board (PCB) may fail to work properly.

Input Damage

This is caused due to the dropping of a printed circuit board or rough handling one. This can happen in different ways. Dropping a printed circuit board (PCB) can cause serious harm. These include cracked components, broken BGA pads, as well as damaged gold fingers. The issue here is that they are usually difficult to locate or identify.

Conclusion

We have been able to cover everything related to PCB repairs. We hope you have gained a lot from this article. To have full understanding read over and over again and take note of the various tips we have explained here.