Introduction to the comprehensive online guidebook written and produced by Circuit Technology Center.
1.1 - Introduction
Circuit boards are more complex today than ever before, but despite how severely damaged they may be, they can be repaired. Indeed the high value of many circuit boards demands that they be repaired. Even less expensive assemblies require repair because just-in-time manufacturing and tightly controlled production runs leave little room for shortage.
Just a few years ago, circuit boards were much simpler and repairs were relatively easy. Today's circuit boards have fine pitch components, ball grid arrays and fine line circuits making them a challenge to repair. Yet, we're driven by simple economics and must repair damaged circuit boards whenever possible. This manual is designed to help you repair and ship good, reliable circuit boards that might otherwise be consigned to scrap.
Because of its high demands, circuit board repair has been accurately compared to surgery. Whether repairing surface mount pads or repairing damaged internal circuitry, the technical knowledge and manual skills needed for high reliability repair and rework are indeed demanding. Since today's repair procedures are more sophisticated than ever before, you need a comprehensive guidebook.
Repair specialists around the world have used this guidebook to repair thousands of circuit boards. Many of the procedures in this guidebook have been pioneered by Circuit Technology Center, the world's leading specialist in circuit board repair and rework services.
Damaged circuit boards may be compared to patients in a hospital. Some will need a stitch or two while others will need open heart surgery. To expect a reliable outcome, each repair project must follow proven and well established procedures. This guidebook covers the repair and rework of both surface mount and through hole circuit boards and assemblies. Not only will this guidebook give you the details for most circuit board repair procedures, but it will also explain why certain procedures are important and answer many questions that you're bound to have.
1.2 - Purpose
This guidebook includes procedures for modifying, reworking and repairing printed boards and printed board assemblies. It complies with standards set by the IPC, in Bannockburn IL. The main IPC documents to refer to when using this guidebook include:
- J-STD-001 Requirements for Soldered Electrical and Electronic Assemblies
- IPC-A-600 Acceptability of Printed Boards
- IPC-A-610 Acceptability of Electronic Assemblies
- IPC 7711 Rework of Electronic Assemblies
- IPC 7721 Modification, Rework and Repair of Printed Boards and Electronic Assemblies
Revision levels for each procedure are recorded in the header section. A complete log of engineering changes is maintained at Circuit Technology Center, Inc..
1.3 - Classes of Product
Three Classes of Products are referred to in this guidebook.
1.4 - Printed Board Types
- Class 1 General Electronic Products
Includes consumer products, some computer products and computer peripherals, and hardware suitable for applications where the major requirement is the function of the completed assembly.
- Class 2 Dedicated Service Electronic Products
Includes communications equipment, sophisticated business machines, and instruments where high performance and extended life is required, and for which uninterrupted service is desired but not critical. Typically, the end use environment would not cause failures.
- Class 3 High Performance Electronic Products
Includes equipment for commercial and military products where continued performance or performance-on-demand is critical. Equipment downtime cannot be tolerated, end-use environment may be uncommonly harsh, and the equipment must function where required, such as life support and critical weapons systems.
Four Printed Board Types are referred to in this guidebook.
1.5 - Conformance Level
- Rigid Printed Boards and Assemblies - R
A printed board or assembly using rigid base materials only. These may be single sided, double sided or multilayered.
- Flexible Printed Boards and Assemblies - F
A printed board or assembly using flexible or a combination of rigid and flexible materials only. May be partially provided with electrically nonfunctional stiffeners and/or cover lay. These may be single sided, double sided or multilayered.
- Discrete Wiring Boards and Assemblies - W
A printed board\assembly using a wire technique to obtain electrical interconnections.
- Ceramic Boards and Assemblies - C
A printed board or assembly using ceramic as the base material with interconnections separated by dielectric.
Conformance Level indicates how closely the repaired or reworked product will be to the original specifications. The Conformance Level listed for each procedure should be used as a guide only. Conformance Levels include the following:
Most closely duplicates the physical characteristics of the original and most probably complies with all the functional, environmental and serviceability factors.
Some variance with the physical character of the original and most likely varies with some of the functional, environmental and serviceability factors.
Significant variance with the physical character of the original and may vary with many of the electrical, functional, environmental and serviceability factors.
Class 3 Products must use procedures rated High unless it can be demonstrated that a lower level procedure will not adversely affect the product's functional characteristics.
Class 2 and 1 Products should use procedures rated High for assured safety and dependability but Medium or Low Level procedures can be used if it has been determined that they are suitable for the specific product's functional characteristics.
Procedures in this manual are given a "Conformance Level" rating which is described in the following table.
TABLE 1 - Conformance Level
No - Procedure may not comply with functional consideration.
|Electrical - Resistance
|Electrical - Inductance
|Electrical - Capacitance
|Electrical - Cross Talk
|Electrical - High Speed Frequency
|Environmental - Shock
|Environmental - Vibration
|Environmental - Humidity
|Environmental - Temperature
|Environmental - Altitude
|Environmental - Bacteria
|Environmental - Fungus
|Serviceability - Future Repair or Mod.
Verify - Procedure should comply with functional consideration but should be tested to verify.
Yes - Procedure will normally comply with functional consideration.
1.6 - Skill Level
In the circuit board manufacturing and assembly environment, most processes are tightly controlled and one-directional. The technicians who run these processes have certain defined characteristics and training. As you look deeper into the repair operation, the first thing that becomes apparent is that an entirely different set of skills is needed. Repair skills are more specific. They require a higher degree of manual dexterity, patience, and a thorough understanding of the repair process. There are more steps involved in any single repair operation than the typical assembly technician would be confronted with. It becomes a personnel issue as well as a training one. You must not only have the proper training program, but the right people.
Repair personnel can't be part-timers and repair circuit boards only one day a week or on a rotational basis with other duties. They should be dedicated to the repair operation and do nothing but repair. For challenging procedures to be done reliably, they must be done repeatedly. Furthermore, some repair skills are so specific that they should be limited to certain individuals who demonstrate an affinity for the job, rather than attempting to train a general number of persons to do the same difficult task.
Considerable supervision is required during the basic phase of the training operation, with lots of individual help and attention. The key is not to attempt to move people too fast on the road to proficiency. It's a step-by-step approach. Regardless of who provides the training, you will find that the greatest cost and investment is in personnel. Personnel are key to the success of the whole operation.
Three Skill Levels are referred to in this guidebook. The Skill Level recommended should be used as a guide only.
1.7 - Tools and Materials
- Intermediate - I
Technician with skills in basic soldering and component rework but inexperienced in general repair/rework procedures.
- Advanced - A
Technician with soldering and component rework skills and exposure to most repair/rework procedures but lacking extensive experience.
- Expert - E
Technician with advanced soldering and component rework skills and extensive experience in most repair/rework procedures.
Repair is and may always be a highly labor intensive operation relying more on individual operator skills than automation. Despite the availability of very good tools for repair, many in-house repair operations are poorly equipped. Here are a few guidelines for the basic equipment needed in an up-to-date repair operation.
- Ergonomic Workstation
Good repair work can't be done at an old workbench or makeshift setup. Performing circuit board repair requires a high degree of concentration and dexterity. A proper workstation that is ESD grounded with proper lighting, outlets, and comfort is therefore essential. When possible, commonly used systems can be bolted to the work surface to improve efficiency.
- High Quality Stereo Microscope
Precision repair cannot be done without a microscope of this type available to the repair operation 100% of the time. Limited access will not do since it must be used constantly. Use of video cameras and monitors, although they may be fine for inspection or training, should be avoided. They cannot provide the clarity that quality optics offer. Also, the microscope needs a good light. Halogen, or fiber optic lighting systems with flexible goose-necks to direct the light are the best for this application.
Precision soldering is vital to modern repair operations. Repair technicians can't get by with the traditional soldering tools that were commonly used as recently as a few years ago. They need the very best soldering irons that are highly controlled, ergonomically designed and feature a wide assortment of small tips.
- Component Removal Tools
Today's expanding variety of large and small components require an array of special use tools and methods for safe, efficient component removal. These tools generally use either conductive heating (by contact), convective heating (by hot gas) or infrared heating (by focused infrared lamps.) Each method has its own advantages and disadvantages depending on the particular application.
- Preheating Station
When possible, you should preheat the entire circuit board before SMT component removal. Preheat minimizes thermal shock due to localized heating in the rework area, and speeds up the rework process. Most facilities have a curing/drying oven, but a preheating station for maintaining heat in addition to the oven is often necessary. A hotplate-style preheater or infrared heater will maintain the temperature of the board after it is taken out of the oven, or can heat the board up from ambient temperature.
Some manufacturers of ceramic chip capacitors recommend that the Preheat Ramp Rate not exceed 2-4 C/Sec.
- Micro Drilling and Grinding Tool
Bulky, hand-held drilling and grinding tools that have both the motor and power supply contained within the hand-piece are difficult to manipulate for the kind of detailed work that is necessary in repair. The type needed is preferably a lightweight, high quality, dental style drilling tool.
- Precision Drill System
Repair and rework projects often require the need to make precise holes, slots, grooves etc. Precision, accurate depth control and high speed are a must. The ideal system should have a base plate to pin circuit boards in place and an optional microscope attachment.
- Replacement Circuits and Pads
Circuits and surface mount pads can be replaced using liquid epoxy, but liquid epoxy can be messy and unreliable when replacing fine pitch pads. Pads are available with a dry film adhesive on the back. These replacement pads and circuits are heat-bonded to the board surface, and are available in any pattern that you might need.
- Gold Contact Plating
Plating gold edge contacts or any metal surface is a serious business. The chemicals used are hazardous and must be handled properly. The power applied to the plating surfaces must be controlled accurately to expect reliable results.
- Base Board Repair Kits and Coloring Agents
For many repair operations you need high strength, high temperature epoxies. You should select a two-part epoxy because they offer the high strength, thermal resistance and durability that one-part and quick-setting epoxies do not have. It is also important to have masks or coloring agents so that you can restore the cosmetic appearance of the board. It is best to cure the epoxies in an oven if possible.
- Eyelets and Eyelet Press
Solder plated copper eyelets and an eyelet press to repair damaged plated through holes is generally required.
1.8 - How To Set Up An In-House Circuit Board Repair Department
It's a fact that far more printed circuit assemblies are damaged during the manufacturing process than they are in the field. And even though circuit boards are more complex today than ever before, they are still repairable. Ten years ago boards were much simpler, and repairs were easy; but the assemblies also cost a great deal less. Today's printed circuit manufacturers and assemblers are driven by simple economics. They must repair damaged circuit boards. The primary question is whether to develop and maintain a full repair department in-house, or to contract the repair out. Which choice makes the most sense?
IPC defines Rework and Repair as follows. Rework - The act of reprocessing non-complying articles through the use of original or equivalent processing, in a manner that assures full compliance of the article with applicable drawings or specifications. Repair - The act of restoring the functional capability of a defective article in a manner that precludes compliance or the article with applicable drawings or specifications.
Repair encompasses much more than simply rework, i.e. removing/reattaching components. You must be prepared to make a real commitment in several key areas if you plan to complete repair work in-house. If not, you are better off contracting the work out to a reputable repair facility. In reality, more damage can be done to a board from a botched repair than from most other causes. Aside from soldering and desoldering, other aspects of repair can include replacing damaged circuits, gold contacts, and SMT pads; re-plating solder-contaminated gold contacts, repairing burns or physical damage to the laminate, repair of through-holes, and more. Both contract manufacturers and OEMs will benefit from establishing a good in-house repair operation.
Five Keys to Reliability
There are five basic requirements needed for successful implementation of a high quality circuit board repair department:
- Documented Standards
The key starting point, of course, is a good set of documented standards. Standards will establish which types of defects are acceptable as is, and which are not. Although most major manufacturers have their own set of acceptance standards, the small manufacturer can obtain commercially-available guidelines, in particular from the IPC. Specific documents include IPC A-600 and IPC-A-610. A good working knowledge of these standards can prevent unnecessary repair.
- Documented Procedures
Every repair operation, whether it be replacing a pad or re-plating a gold contact, requires a specific set of procedures. The goal of this book is to provide you with a detailed explanation of each procedure. If you need more information, an excellent additional reference source are the IPC's publications IPC-7711 Rework of Electronic Assemblies, and IPC-7721 Repair and Modification of Printed Boards and Electronic Assemblies. These IPC publications, along with this Guidebook, should be an integral part of your repair department and can serve as a tool for training repair personnel. To obtain copies of these publications, contact the IPC. Copies can also be obtained from Circuit Technology Center, Inc..
Once you know what can be repaired and have the necessary guidance to proceed, the next step is completing the repair, and that requires qualified personnel. Of course, even the most highly skilled technicians require training if they are to perform their best. For your Rework and Repair Program to obtain successful results, operators and technicians must be properly trained.
- Comprehensive Training
Repair personnel can't be part-timers and repair only one day a week or on a rotational basis with other duties. They should be dedicated exclusively to the repair operation. The reason for this is to develop a high level of skill and maintain it through repetition. For many challenging aspects of repair to be done reliably, they must be done repeatedly, such as the replacement of fine-pitch surface mount pads. Furthermore, some repair skills are so specific that they should be limited to certain individuals who demonstrate an affinity for the job, rather than attempting to train a general number of persons to do the same difficult task.
Considerable supervision is required during the basic phase of the training operation, with lots of individual help and attention. The key is not to attempt to move people too fast on the road to proficiency. It's a step-by-step approach. Other companies may do it differently, but this is our method. Regardless of who provides the training, you will find that the greatest cost and investment is in personnel. Personnel are key to the success of the whole operation. Equipment costs are actually quite low in comparison.
- Modern, Up-To-Date Equipment
Repair is and may always be a highly labor intensive operation relying more on individual operator skills than automation. Despite the availability of very good tools for repair, many in-house repair operations are poorly equipped.
- Highly Skilled Technicians
In the circuit board manufacturing and assembly environment, most processes are tightly controlled and one-directional. The technicians who run these processes have certain defined characteristics and training. As you look deeper into the repair operation, the first thing that becomes apparent is that an entirely different set of skills are needed by repair personnel compared to assembly personnel. Repair skills are more specific. They require a higher degree of manual dexterity, patience, and a thorough understanding of the repair process. There are more steps involved in any single repair operation than the typical assembly technician would be confronted with. It becomes a personnel issue as well as a training one. You must not only have the proper training program, but the right people.
Procedure for reference only.