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Here is a lead test with a long history. (Write or call off-line if you  have 
questions).
 
 
Number: 
Date: 
Revision: 
Subject: Surface Lead Contaminant Detection Spot  Test 
1.0 Scope 
1.1 This  simple and rapid non-destructive colorimetric spot test method is 
for use in  determining if non-ionic lead (primarily lead oxide) contaminant is 
present on  bare printed wiring board and completed assembly surfaces.   
1.2 The  test will not identify the particular compound of lead present on 
the surface  tested nor separate mixtures of various lead compounds on the 
surface.  After a functional problem is found with  boards or assemblies, usually 
failure at elevated temperature and humidity, this  test can be used to confirm 
or eliminate non-ionic lead contaminant as a root  cause. 
1.3 The test  can detect lead levels easily in the 0.1 microgram range.  
Lower levels in the presence of  interferring metals can be detected by a skilled 
operator using accurate  standards. 
2.0  Applicable Documents 
IPC-TP-135   "Insulation  Resistance Degradation by Non-Ionic Surface 
Contamination-- Its Cause &  Cure." 
Feigl , Fritz, and Suter, Hans A., “Analytical  Use of Sodium Rhodiazonate”, 
  Industrial  and Engineering Chemistry, Vol. 14, No. 10, 840-2,  (1942). 
3.0 Test Specimen 
3.1 A bare  printed wiring board or completed assembly at least 50 mm x 50 mm 
x  thickness. 
4.0  Apparatus & Materials 
4.1 Sodium  rhodizonate 
4.2  Tartaric  acid 
4.3 Sodium  bicarbonate 
4.4 Cotton  tip swabs 
4.5  Indicator dropper bottle 
4.6 Balance  capable of weighing to 0.001 g. 

5.0  Procedure 
5.1  Preparation 
5.1.1 Prepare  the stock buffer solution by dissolving 15 grams of tartaric 
acid and 19 grams  of sodium bicarbonate in one liter of distilled water.   The 
pH of the resultant buffer  solution should be 2.79.  This  solution is 
stable, and can be stored for an extended time in the  laboratory. 
5.1.2 Prepare  the 0.2% sodium rhodizonate indicator solution by dissolving 
0.01 g. of sodium  rhodizonate in 5 ml. of water.  Place the solution in the 
indicator dropper bottle.  [Note: the useful life of the indicator  solution is 
approximately 8 hrs.] 
5.2  Test 
5.2.1 Using a  clean cotton swab, place 2 drops of buffer solution on the 
cotton swab.   
5.2.2 Rub the  buffer soaked swab on a dielectric area (non-plated area) of 
the printed wiring  board or assembly surface, being sure not to touch the  
traces. 
5.2.3 Using a  second clean cotton swab, place 3 drops of the indicator on 
the cotton swab.   
5.2.4 Rub the  indicator soaked swab in the area coated by the buffer  swab. 
5.3  Evaluation  
5.3.1 Any  color change from yellow to red on the indicator swab indicates a 
positive test  for lead contaminant.   
5.4 Action 
5.4.1 The  boards or assemblies should also be tested for the presence of 
organic non-ionic  contaminant using the test methods cited in 2.0. 
5.4.2 The  lead contaminated boards or assemblies can be recovered by 
applying and curing  the lacquer described in 2.0, then washing it off using a 
suitable cleaning  agent.  
5.4.3 The  organic non-ionic contaminated boards or assemblies can be 
recovered per methods  cited in 2.0 
6.0 Notes 
6.1 The  tartaric acid, sodium bicarbonate and sodium rhodizonate used in  
this method can be obtained from standard chemical supply houses.  Reagent grade 
chemicals are  preferred. 
6.2 The  literature claims this test can be used to detect the presence of 
stannous tin  (+2 oxidation state) by a color change to violet, however, stannic 
tin (+3  oxidation state) gives no change. 
Originally Drafted by:            W. G. Kenyon            April, 1998      
Revised:                                 W. G. Kenyon            March, 2005 


Bill Kenyon
Global Centre Consulting
3336 Birmingham  Drive
Fort Collins, CO 80526
Tel: 970.207.9586 Cell:  970.980.6373
email: [log in to unmask]


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