Ask Helena & Leo

Question: IPC-610 has many areas that are left to ones interpretation. The area for solder touching glass body components is one of them. The IPC mentions this along with the subject of maximum fillet height and the image that sets in some peoples minds is that it’s just a defect if solder is only touching on top of the body as stated on other body styles. Please give clarity that solder should not touch any component body except for SOIC’s and SOT’s?

Answer: Thanks for the question as it forced me to not only ask our instructor who is in house, but also to call other members of the IPC committee to get their inputs and position regarding solder touching the glass body of glass bodied components.

There are basically two conditions where solder will touch the glass body, one, too much solder on the pad, and two incorrect pad design.

The documents, J-STD-001 and IPC-A-610 are assembly documents and they address the reality of what is being inspected. Hence, if a condition is found to be defective or non conforming, then the condition has to be rejected and dispositioned as to how it is to be handled, i.e., scrap, rework, use as is, etc..

As mentioned in our conversation Note 5, in Table 7-5 of J-STD-001 states, “The maximum fillet may overhang the land or extend onto the top of the component termination; however the solder does not extend further on the component body”. The same note is also in Table 8.3 of IPC-A-610.

The interpretation of the terms, “…solder does not extent further on the component body” is not just for excess solder coming over the top of the component body, it is for any solder touching the component body, being either the bottom of the component, the sides of the component, or the top of the component. Cylindrical End Cap terminations, due to their design, allow more capillary action up into the center of the circle of the end cap, which by its circular shape, allow narrower solder collection on the sides and the bottom of the component end cap diameter. An example of this can be seen in Figure 8-58 and 8-59 of the IPC-A-610 document.

The situation at times is that the solder does touch the bottom of the glass component due to the pad or land size and the orientation of those pads due to the design of the product and the position of the component on those pads. This is defined as a design condition and typically it is accepted, as it is due to the design of the product. The problem however, is knowing the application of the product and whether or not it is to be used in a harsh environment or in a business environment, be it both class 3 requirements, prior to making the disposition decision. The IPC specification cannot address usage application as this is a design concern and has to be addressed in the design stage of the layout of the artwork. This is where a Material Review Board decision has to be made to disposition the condition as mentioned above. J-STD-001 and IPC-A-610 address the actuality of the condition and the membership consensus vote from day one of the publication of these documents is solder has not been allowed to touch the body of glass bodied components.

The hot solder touching the glass body will cause a shock to the glass, potential causing the glass to crack or craze, which would cause a latent failure of the component.

The same reasoning also applies to through hole component glass body diodes where the solder is not allowed to touch the body of the component. The reasoning is the same, thermal shock to the component.

I realize this is a difficult thing to observe, but the design of the product has to be specific in the pad layout design to minimize and eliminate this condition from occurring.

I recommend working with your supplier to help resolve this issue.