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Recent Ask the Experts Questions
September 23, 2019
Gold Edge Contact Rework
I am replating gold edge contact that need repair. After completing the bench-top replating process the board meets the required thickness specifications and passes a peel test.

However, the electroplating process leaves slight dark residue on the gold contacts. Is this acceptable? Can it easily be removed?
September 20, 2019
ESD Grounding - 1 Meg Ohm Resistor
Why do we need to use a 1 meg-ohm resistor for ESD grounding?
September 19, 2019
Components Falling Off During Reflow
Can excessive solder paste volume contribute to components falling off the bottom of the circuit board during topside reflow?
September 18, 2019
Class 3 Pin Contact Question
I am working on a class 3 product. We have an assembly from one operation that has a tinned pin. The pin is inserted into a gold plated socket on the next assembly.

This bothers me to no end but no one on the program seems to care. Does this meet class 3? What do you say?
September 17, 2019
Out-gassing and Cleaning
I have created a series of PCBs with no solder mask. I will be soldering 2 spring pins, a 0805 ceramic capacitor and a 0805 resistor to each board. There are 40 PCBs in the stack.

The stack will be installed in a vacuum chamber. Out-gassing from the cleaning solution is a concern.

Do have a recommended process for cleaning the PCBs that will not out-gas when installed into a vacuum chamber?
September 16, 2019
Options for Reballing BGA Components
Which of the following do you recommend when reballing BGA components?

Reballing with solder paste and solder spheres, or with solder spheres only?

Would you change the process depending on the size of the BGA component or number of balls?
September 15, 2019
Critical Part Fixture During Reflow
I'm populating a PCA with a component that has critical placement requirements. My pick/place machine does not have epoxy dispensing capabilities. I'm interested in using a fixture to hold the part in place while it goes through the reflow oven. Is this a wise practice? Are there standard fixtures for this process?
September 15, 2019
Aluminum Trays and Rapid Static Discharge
Occasionally we transport assembled circuit boards directly on aluminum trays. Some in our plant are concerned that the aluminum surface may discharge static charges too quickly. I'm familiar with this concern, but wonder about all the assembly and test machinery we use where assembled circuit boards come in contact with various metal surfaces. Should we be concerned when transporting assembled circuit boards that lie directly on the surface of aluminum trays?
September 13, 2019
Reusing recovered solder paste
We are an EMS operating mainly in automotive, industrial and lighting electronics segments. We are assembling PCBAs with 0201 component, a few BGAs, QFPs and SMD LEDs etc.

During the paste printing process, we are wasting a lot of solder paste due to changeovers and small production runs.

Is there any way to recover the solder paste, since disposition of used solder paste is tedious task? Is it OK to re-use it after mixing of fresh and used paste in 1:1 ratio?
September 12, 2019
What Caused SMT Pads to Oxidize After Reflow
After our boards (ENIG) were run through reflow, the assembler is stating that the through hole/SMT connector pads oxidized.

We specified ENIG to our fabricator but are not 100% sure that is what we received.

Is there a possibility that any other finish would oxidize after reflow? Or after reflow any cleaning could cause this problem?