Quality tests for Printed Circuits Boards

Quality tests for Printed Circuits Boards

The Printed Circuit Boards (PCBs) are very sophisticated and complicated items which are of utmost importance in the smooth operation and sustainability of the electronic machinery and it would not be an overstatement to say that even the slightest of faults in a PCB can bring the working of fundamental machinery to a standstill. In this scenario, it is of vital to have approved standards of quality control for the manufacturing, development and operation of the Printed Circuit Boards (PCBs). Some of the standard tests performed in order to ensure the quality of the Printed Circuit Boards (PCBs) are as follows,

    1)      100% Electrical Test

    2)      100% Visual Inspection

    3)      Dimensional Inspection

    4)      Micro Section

    5)      Solder Ability Test (245+-5C) , 10 sec

    6)      Thermal Test (288+-5C)

    7)      Tape Test

    8)      Peel Test

    9)      Impedance Test

    10)  Ionic Contamination Test

     1)    100% Electrical Test

Electrical testing is of utmost importance for a PCB which involves the electrical testing of various aspects of the Printed Circuit Boards (PCBs). In electrical testing every “Node” on the PCB board is tested. Short circuit tests are performed to be if any part of the PCB is short circuited. Clam shell tests are performed to obtain the simultaneous testing of both sides of the PCB in case of double sided Printed Circuit Boards (PCBs). Continuity tests are performed to check if the resistance between the tests points is within specified limit.  Some of the other tests performed in Electrical testing of the Printed Circuit Boards (PCBs) are flip test, high pot test, impedance control test, leakage test, opens test and optimized net list tests.

     2)    100% Visual Inspection

Visual tests are performed using AOI machines to check if all the components after the Printed Circuit Boards (PCBs) assembly process are there where they are supposed to be. The AOI machines use high resolution cameras aided with software Gerber and drill files to make the comparison on the Printed Circuit Boards (PCBs).

3)    Dimensional Inspection

Dimensional inspection is necessary because the size and dimension of the Printed Circuit Boards (PCBs) is specified as per the design of the device in which the PCB has to be used in. The dimensional test compares the physical dimensions of the PCB against the software provided design of the PCB.

    4)    Micro Section Testing

The micro testing of the Printed Circuit Boards (PCBs) is performed in order to check the drill via on the PCB. Via are micro sized in PCB and have to be carved with greatest care as slight offset in via can be of serious design and operation faults. 

    5)    Solder Ability Test

It is our understanding that components are soldered on the PCB during the Printed Circuit Boards (PCBs) assembly process therefore it is necessary to check the durability of the solder through the solder ability test. The solder has to withstand high temperatures and extreme working conditions without showing any signs of deterioration. The solder tests are performed up to 245C for 3 seconds to check the response of the solder. If the able to withstand such conditions, only then it passes the solder ability test.

     6)    Thermal Ability Test

During the working of Printed Circuit Boards (PCBs), extreme conditions can arise which can lead to heating of the inner core. In such cases, the Printed Circuit Boards (PCBs) should be able to withstand the extreme heating. Thermal ability tests are performed by subjecting it to temperatures up to 288 for about 10 seconds to check its performance.

7)    Tape Test (adhesion test)

Tape tests are performed to check the adherence of the copper foil on the PCB. The tape is applied to the Printed Circuit Boards (PCBs) and peeled off in order to check if any copper foil residue adhered to the tape. The Printed Circuit Boards (PCBs) is only passed for further processing if no copper residue adheres to the tape.

     8)    Impedance Test

Impedance testing is done in order to check the impedance between different nodes and the components of the Printed Circuit Boards (PCBs). The impedance should not be offset to the specified limits.

     9)    Ionic Contamination Test

The Printed Circuit Boards (PCBs) during manufacturing and developing process can be contaminated with ionic impurities which can lead to the decrease in the impedance of the Printed Circuit Boards (PCBs) which can cause operational ambiguities. In order to avoid any unforeseen circumstances, the ionic contamination tests are performed.

Metal Core Printed Circuit Boards

Metal Core Printed Circuit Boards

Printed Circuit Board (PCB) can be classified into three categories if the criteria of classification were to be made the core material of the PCB. The Printed Circuit Board (PCB) are available in ceramic based core material, FR-series or fire retardant series of the core material and the Metal core Printed Circuit Board (PCB) or most commonly known as MCPCB. The most commonly used Printed Circuit Board (PCB) is standard FR4 boards which have various fire retardant material as their core. FR4 or FR-4 is a NEMA used for the glass reinforced epoxy laminate material which is commonly used in standard Printed Circuit Board (PCB) used in the PCB industry.

Ceramic Printed Circuit Board (PCB) or CPCBs

The second type of PCB is the ceramic Printed Circuit Board (PCB) or the ceramic core PCBs. The ceramic PCBs are used for high temperature, pressure, frequency operations. They provide greater insulation and are highly reliable as compared with other type of the PCBs. The ceramic Printed Circuit Board (PCB) are mostly used for minor volume production of the electronic devices as for high volume production it is more economical to use the standard FR-4 type PCBs. The composition of ceramic Printed Circuit Board (PCB) is usually alumina aluminum nitride and beryllium oxide. The conducting material used in ceramic Printed Circuit Board (PCB) is either copper or silver palladium. 

Metal Core Printed Circuit Board (PCB) or MCPCBs

The third type of the Printed Circuit Board (PCB) is the Metal Core Printed Circuit Board (PCB) or MCPCB. The metal core PCBs have some metal as their core which mostly range from Aluminum, Copper and steel alloy. All three metal cores have either own advantages and are used for their specialized purposes. The aluminum core has greater heat transferring and dissipating capabilities and it is also relatively cheaper as compared with copper and silver. Copper has better overall properties as compared with aluminum but it is more expensive. Steel is more rigid and provides greater stability to the core as compared with aluminum and copper but its conducting properties are inferior as compared with copper and aluminum. Making the comparison, it can be analyzed that aluminum is more suitable and economical to be used as compared with silver and copper, so most of the Metal Core Printed circuit boards make use of the aluminum core.

The metal core PCBs are also referred to as the metal backed PCBs, metal base or metal clad PCBs.

Advantages of Metal core Printed Circuit Board (PCB)

The main advantage of Metal core Printed Circuit Board (PCB) over ceramic and FR-4 type of Printed Circuit Board (PCB) is their ability to dissipate heat more efficiently away from the components on the circuit board, hence in turn saving the components from overheating and damage. In most LED applications, metal core Printed Circuit Board (PCB) is used because of its ability to dissipate heat generated in the LED circuitry. In this case if the heat were not properly dissipated, it would cause severe damage and output inefficiency for the system. In this case, the main purpose of the metal core is to dissipate the heat away from the board so as to protect the system.

The second advantage of the metal core Printed Circuit Board (PCB) over the other kind is their better coefficient of thermal expansion. Thermal expansion and contraction is the inherent nature of the material and most material suffer from it. The aluminum core Printed Circuit Board (PCB) on the other hand has greater ability to without such changes under severe circumstances.

The third bigger advantage of the metal core Printed Circuit Board (PCB) is their dimensional stability. Even at high temperatures and severe conditions, the size change of the metal core PCB is minimal as compared with the other type of the PCBs.

Applications of Metal Core Printed Circuit Board (PCB)

The metal core Printed Circuit Board (PCB) are used in major applications such as LED lights, cars, amplifier and audio systems, printers, switching electronic devices.

The metal core Printed Circuit Board (PCB) is also further divided into five categories depending on the location of the metallic core and the layers of the Printed Circuit Board (PCB). The five categories are named as single layer, chip on board, double layer, double sided and multi layer metallic core Printed Circuit Board (PCB).