Bare Board Electrical Testing Capabilities
Bare Board Electrical Testing CapabilitiesMOKO, as a regular part of
its manufacturing process, performs electrical testing on your printed
circuit boards to ensure their quality. Below please find a full
explanation of how we perform these tests and what they mean. As a
leading PCB manufacturer we assure you that we monitor for quality here
in our own facilities, where we fabricate your boards; we are not a
broker. Your order is manufactured by us and tested by us so you will
know that your printed circuit boards are free of defects and meet the
standards you expect.We currently have two different
types of testing equipment available to test your circuit boards; we
have a number of Everett Charles ATG test machines that are flying
probe, fixtureless testers and we also have universal grid testing
capability. These machines use fixtures built specifically for your PCB.Bare board testing involves using capacitance and resistance tests;
each of our machines uses a combination of both. Capacitance testing for
a bare board involves testing for opens and shorts by "charging" a net
or plane and then probing each net to measure the induced capacity.
Inaccuracies occur with this method because of the inherent variability
in producing circuit boards. However field measurement or field effect
testing for shorts uses a very similar approach.Resistance testing measures the resistance found in the net. As
electric current flows through a conductor collisions between electrons
and atoms interfere with the flow of the electrons. This is known as
resistance and it's measured in ohms.A good conductor has LOW resistance - at common temperatures silver
is the best conductor and copper is second. The amount of resistance
depends on the conductor's length and its cross-sectional area. If you
have two circuits of the same material and the same cross-section and
one is twice as long as the other - the longer one has TWICE as much
resistance. If you have two circuits of the same material and the same
length but one is twice as thick as the other - the thicker conductor
will have HALF the resistance.So Resistance is proportional to length and inversely proportional to
the cross-sectional area of a conductor and dissipates power in the
form of heat.MOKO' test processes use CAD/CAM data for ALL test
programs and optimize both ATG and Trace test programs while meeting
Class 2 requirements. We follow the IPC 9252 specification guidelines
for Class 2 testing processes, which means that we test 100% of the
networks on the board for continuity and isolation (that's opens and
shorts) using a test program generated from your Gerber data. We do not
test 100% of the points - we optimize out mid points of nets as allowed
by the standard. We do not use your original Gerber data - it does not
guarantee a 100% test.Electrical Test Terminology100% Net List Test: Check of every "node" on every net on the board.Adjacency Test: Type of test for checking isolation
between conductors - shorts test. A software generated program that
checks for nets that are within a tolerance set by the user. Two methods
are used - Proximity Adjacency and Line of Site Adjacency.Clam Shell Test: Provides simultaneous testing of
both sides of the board at the same time. These types of fixtures are
used on single grid testers and dual grid testers. A very reliable
method of bare board testing because all points are tested at the same
time.Combined Grid/Probe Testing: Using the flying probe
test sequence to cover areas of the board with fine pitch, high density
points while the grid test verifies power to ground separation, through
hole and wider pitch component pads.Comparative or Golden Board Test: Method using a
"master" or known good board (KGB) to learn a program and then test
other boards against the learned net list program. Poor choice for test
accuracy - you may be learning a "bad" board.Continuity Test: Verification that the resistance
between test points is lower than the specified limit or maximum
continuity resistance. See shorts and opens tests.End of Net: A feature which is either the origin or the termination of a conductor network.Endpoint: A test point or node required to be tested to meet the 100% continuity and isolation test.Field Effect and Field Measurement Test: Refer to a
type of test that uses large nets as antennas to send a specific high
frequency alternating current at a specific voltage. The remaining nets
are checked and those that have similar voltages for all antennas are
considered as shorted and then retested using Ohm's law resistance to
verify the shorts.Flip Test: Consists of two separate, independent
single sided tests on a universal grid. Testing one side and then the
other. Unless a significant number of points are tested during both
tests it can be a very inaccurate method.High Pot Test: Refers to high voltage potential
testing to check for high resistance continuity or leakage between
ground and power planes. DC voltages in the 500 to 1000 volt ranges are
used for a specified dwell time.Impedance: The design of a circuit and the frequency
of the current passing through it have various affects on the
alternating current passing through it. The combination of these effects
and the resistance of the conductor is called impedance.Impedance Control Test: A device called a TDR (Time
Domain Reflectometer) is used to check circuits to determine if they are
within expected tolerances. Conductor length, spacing, width, height
and separation affect the impedance.In Circuit Test: Test performed after components are installed - a check for shorts or opens caused during assembly operations.Isolated Land: A test point not connected to any other test point or net. Also called a single point net, singlet or no connect.Isolation Resistance: The resistance tolerance between the circuit board's non-connected traces and/or lands.Land: A portion of a conductive pattern usually used
for connection, component attachment or both. Surface mount pads,
component hole pads, gold fingers etc.Leakage: Movement of current between two conductors
that are not connected and therefore should be isolated by a minimum
amount of resistance. Causes significant "noise" in the properties of
the circuit board.Mid Net Point: A feature which is a not at either the termination or origin of an interconnecting networkNet: An entire string of points or connections from the first source point to the last target point including lands and vias.Net List: A list of alpha-numeric locations, used to describe a group of two or more points that are electrically commonNode: A connection point between a network and an off- the-board item like a component or test probe. See LandOpens Test: Check to make sure there is current flow
from one "node" to the next for every net on the board, again by
measuring the amount of resistance of the conductor.Optimized Net List Test: Check every "end of net" for all nets on the board and selected intermediate nodes on the board.Shorts Test: Check to make sure that NO current flows between separate nets by measuring the amount resistance between them.
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