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Recent Ask the Experts Questions
November 15, 2019
Through Hole Connector Solder Joint Hole Fill
When looking at IPC610D in relation to through hole connectors and Class III level soldering.

What is the recommended inspection method to ensure the 75% fill requirement is being met? For many through hole connectors one side is totally covered.
November 14, 2019
Challenging Cleaning Problem
We are designing an ECG monitor that uses an embedded phone-modem LGA module. This phone modem is shielded, however, it is not hermetically sealed. The manufacturer requires that the board not be washed, or that a method of the user's choice be used to prevent ingress of contaminants, wash water, etc.

The same board will also have ECG circuits with high impedance differential amplifiers. The ECG circuits must avoid conductive leakage. Normal industry practice on ECG/Instrumentation boards is to always clean.

The board has several BGA processors and ASICs, uses 3 to 5 mil traces, has 0402's, and could possibly have a need for BGAs on both primary and secondary board sides.

What is the best way to assemble the LGA phone module onto the board in a low volume scenario, 1000 to 3000 units/month?
November 13, 2019
Selective Printing for BGA Components
We use common BGA packages on many of our low-end products. To save cost, could we print paste only on the pads that have functional requirements?

For example, could we print all the perimeter pads on a 120 pin BGA, but skip printing on 50 or more of the interior pads since they serve no function?
November 12, 2019
How To Measure Solder Paste Rolling Diameter
A customer has asked us to measure the rolling diameter of solder paste while printing with our automated stencil printer.

Is there a way to do this? What is the impact if the rolling diameter of solder paste is larger or smaller than some ideal?
November 11, 2019
Considering Plasma Cleaning
We build microelectronic circuits with various small pitch flip chip die's and an assortment of passive components.

To improve underfill flow and better overall circuit cleanliness, we are considering plasma cleaning.

Is there any downside to plasma cleaning? I know in the past there were ESD concerns and we steered away from it.
November 8, 2019
Reliability of Automated Soldering vs. Hand Soldering
On occasion, we have had to place a skip in our SMT placement machine due to unavailability of a surface mount component. The intention is to build the circuit card assembly and then hand place and solder the missing components when available. I accept that there are times when you have to rework/touch-up/replace components, but these should be kept to a minimum.

Can you comment on the potential differences in reliability for SMT machine placement followed by reflow soldering vs. hand placement followed by hand soldering of surface mount components?
November 7, 2019
Removal of Non-functional Pads from Inner Layers
Should we remove non-functional pads from inner layers. In some cases, it may be necessary to free up space between rows of pads to route additional trace data. I've read articles that favor both options. What is you opinion?

November 6, 2019
What is Causing Solder Joint Cracking?
We are seeing field returns after a year in the field due to solder joint cracking on the pins of a 16 pin through-hole connector. The boards are used in an automotive dash board application.

What might be the cause of the joint cracking? The connectors are soldered manually. Could selective soldering provide more consistent solder joints and thus reduce or eliminate the cracking?
November 5, 2019
Profiling for Double Sided BGA
We are about to produce double sided BGA boards - BGA components on both sides. What advice would you give for profiling? What advice would you give for reworking?
November 4, 2019
Spotting After DI Water Cleaning
We have a close loop 3 Bed DI System fitted with a resistivity monitor. When the beds are new we generally generate water at approximately 18 Mega Ohms. This system was performing well until recently. We had been running 2-3 months between bed changes, now we are changing the beds out every 2 weeks.

We are seeing visible spotting on surfaces yet the puzzling thing is that the water resistivity reads 18 Mega Ohms. This spotting immediately goes away after a bed change. We've double checked the resistivity meters. Do you have any idea what may be causing this?