CIRCUIT BOARD
CLEANLINESS TESTING
Contamination of circuit boards can bring about severe
degradation of insulation resistance and dielectric strength. Cleanliness of
completed circuit boards is, therefore, of vital interest.
For those companies who have established circuit board cleaning procedures,
the MIL Spec P-28809 has been used as a guideline for control. Now a simple
"on line" test for the relative measurement of ionic contamination has been
developed.
This fast and economical method for testing circuit board cleanliness uses a
Myron L ULTRAMETER™ 4P or 6P, a suitable container and a mixture of Dl (deionized)
water and alcohol. Click here for specifications
and pricing. The
procedure is as follows:
1.Mix a stock quantity of solution using 25 parts by volume of Dl water and
75 parts by
volume of 99% isopropyl alcohol. The conductivity, measured with the
ULTRAMETER™
4P or 6P should be a maximum of 0.166 micromhos/cm.
2.Measure out an amount of the water/alcohol mixture equal to 100 ml per 10
square
inches of circuit board surface to be tested (considering both sides of the
board but not
components) and add 60 ml additional. In other words: 2(L X W) (10ml) + 60
ml = total
solution needed.
3.Fill a poly "zip-lock" bag or other suitable plastic or glass container
with the measured
water/alcohol solution.
4.Using the measured water/alcohol solution in the poly bag, rinse out the
ULTRAMETER's
cell cup three (3) times, discarding the rinse solution each time. Fill the
instrument's cell
cup a fourth time and take a meter reading. This value should be 0.166
micromhos/cm
or less and is the very clean control (or "comparison") reading for the
test.
5.Being very careful not to contaminate the PCB, totally immerse the circuit
board in the
solution. Seal bag. Allow it to soak for three (3) minutes with mild
agitation.
6.At the conclusion of the soaking, pour the solution directly into the
instrument's cell cup
four (4) times; take the fourth reading.
7.Compare the control reading in Step 4 with the reading taken in Step 6.
The higher the
difference between the two readings, the greater the ionic contamination.
Record this
final extract reading for comparison with other boards tested in the same
manner.
The level of cleanliness needed or desired can only be determined by each
individual
company. Mil Spec P-28809 can be used as a guideline or standards can be
established
based upon available data. In either event, the comparative method using the
Myron L
ULTRAMETER™ will assist in the determination of that level of cleanliness.
| Problem |
Solution |
Best Myron
L models |
| High water, sewer use and
waste treatment costs |
Myron L CONTROLSTIK™
Rinse Tank System will automatically monitor the quality of rinse water
and reduce usage by as much as 80%. |
595 or 597
758II-XXX |
| Need to quickly verify DI
water purity or trouble-shoot reverse osmosis equipment. |
Portable conductivity
instruments are easy to use, yet accurate and reliable enough for field
testing of ultra-pure water. |
Ultrameter 4P & 6P, EP ( 5
microsiemen range: 1 resistivity range)
532 T2
(3 ranges ppm/TDS) |
| As DI cylinder are used,
quality decreases falling below acceptable limits. This is not always
noticed before cylinder can be replaced. |
A Myron L continuous
conductivity, resistivity monitor/controller or Aquaswitch. When DI
cylinders approach exhaustion, alarm solenoid valve, etc can be
activated. |
758II-101
753II-II
Aquaswitch I or II |
Conversion Table
| Specific Resistance in Ohms |
Specific Conductance in
Micromhos |
Sodium Chloride Equivalent
in Micro Grams/CM² |
Sodium Chloride Equaivalent
in Micro Grams/In² |
PPM Sodium Chloride |
| 10 megohms |
0.10 |
0.31 |
2.00 |
0.021 |
| 9 megohms |
0.11 |
0.34 |
2.22 |
0.026 |
| 8 megohms |
0.12 |
0.39 |
2.50 |
0.033 |
| 7 megohms |
0.14 |
0.44 |
2.85 |
0.041 |
| 6 megohms |
0.16 |
0.52 |
3.33 |
0.052 |
| 5 megohms |
0.20 |
0.6 |
4.00 |
0.068 |
| 4 megohms |
0.25 |
0.78 |
5.00 |
0.091 |
| 3 megohms |
0.32 |
1.00 |
6.45 |
0.130 |
| 2 megohms |
0.50* |
1.56* |
10.06* |
0.207* |
| 1 megohms |
1.00 |
3.10 |
20.00 |
0.440 |
| 775,000 |
1.29 |
4.00 |
25.80 |
0.575 |
| 620,150 |
1.61 |
5.00 |
32.25 |
0.725 |
| 517,000 |
1.94 |
6.00 |
38.71 |
0.878 |
| 443,000 |
2.26 |
7.00 |
45.16 |
1.027 |
| 388,000 |
2.58 |
8.00 |
51.61 |
1.176 |
| 345,000 |
2.90 |
9.00 |
58.06 |
1.324 |
| 310,000 |
3.22 |
10.00 |
64.52 |
1.476 |
*Equivalent to 0.01 milligram NaCl/In²
(MIL-P- 28809 maximum contamination level)
Note Figures approximated to second decimal place.
|
