Printed Circuit Board Assembly & PCB Design SMT Electronics Assembly Manufacturing Forum

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


Pat Copeland

#14687

5 micrograms | 14 August, 1998

Electrical Eng. is looking for 5 micrograms per sq centimeter. After the board has been cleaned. Is this possible on a fully assembled bd?

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Mike Konrad

#14690

Re: 5 micrograms | 14 August, 1998

5 micrograms per sq. cm. is actually not too clean. The maximum military allowed post-clean, on-board contamination is 5.7 micrograms of NaCl /cm squared (when using the Zero-Ion brand ionic contamination tester). We are use to seeing cleanliness results between 0.0 and 0.5.

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Upinder Singh

#14689

Re: 5 micrograms | 14 August, 1998

| Electrical Eng. is looking for 5 micrograms per sq centimeter. After the board has been cleaned. Is this possible on a fully assembled bd? Yes, u can go to the mentioned level of cleanliness.....but can u be a bit more elaborative. Recently I did stabalize a process with very tight standards and that too without cleaning. Upinder

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Bob Willis

#14688

Re: 5 micrograms | 15 August, 1998

| Electrical Eng. is looking for 5 micrograms per sq centimeter. After the board has been cleaned. Is this possible on a fully assembled bd? The European standard often quoted is 1.5 mg/cm which ia achievable on a board assembly please remember one of the forfotton causes is the solder mask. Solder masks can leach out ionic material during the testing. Speacially if you use heated solutions like the Alpha test equipment. The comment about no clean is also true with some work you can read leas than the specification without cleaning in nitrogen soldering.

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Bob Willis

#14691

Re: 5 micrograms | 17 August, 1998

| 5 micrograms per sq. cm. is actually not too clean. The maximum military allowed post-clean, on-board contamination is 5.7 micrograms of NaCl /cm squared (when using the Zero-Ion brand ionic contamination tester). | We are use to seeing cleanliness results between 0.0 and 0.5. Here is a test method for practical testing of circuits see what you think. 1. Select a printed board assembly and a location for test with two terminations approximately 0.010" apart. 2. Apply one drop of distilled water across the two terminations. The distilled water should be confirmed at 1meg H2O. 3. Connect a power supply to the two terminations with a 3-5 volt supply. A lower or higher voltage may be used if the products being assessed normally use a different voltage. All tests should be conducted at a single voltage to aid comparison. 4. The circuit board cleanliness may be based on the growth of copper dendrites across the terminations or by monitoring the current and should be <300 micro amp�s after 1 min. Using a 5-10X magnification the reaction if any may be observed between the adjacent terminals. 5. When the test is complete the water and any reaction products may be removed. The circuit board may then be used in an undamaged state. 6. Repeat the test on another area of the board. 7. The test may be used on bare boards, soldered and cleaned boards, con formally coated boards or boards using a no clean process. The test is very sensitive and is an ideal method of assessment but it does not currently relate and can not be compared to existing cleanliness standards. The tests may be conducted and then compared with long term SIR tests or ionic contamination measurements. It is possible to conduct the different tests and compare the results and then set an internal reference criteria. Bob Willis EPS

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