Assemblies
Screening and Qualification Documents
A method number points at a written procedure. It says the described test was passed under the described conditions, and nothing more.
A screening line on a datasheet names a written test method, by number. Read as a citation, it makes one claim: the described test was run on that part, under the conditions the document sets, and the part passed. It is not a performance figure and it is not a prediction of service behavior. The number is the pointer; the document behind it carries every condition that gives the line meaning.
A method number is a citation, not a result
A datasheet compresses evidence into a few columns, and the screening line is the most compressed entry on the page. It does not describe the test. It points at a public document that does: the fixture, the sequence, the levels, the acceptance criteria. What the citation certifies is that the described test was passed under the described conditions, neither more nor less.
That framing matters as soon as two datasheets sit side by side. Two lines citing two different method numbers are not two intensities of one guarantee. They are two procedures, and the distance between them is written in the documents, not on the page. A reader who does not open those documents is comparing typography.
Which family does a method number come from?
Test methods are published in families, each scoped to a class of hardware. A number quoted without its family is an incomplete citation, because the same short phrase can name different procedures in different documents. Four public families cover most of what turns up on control component datasheets.
| Family | Scope | What citing it establishes |
|---|---|---|
| MIL-STD-202 | Test methods for electronic components | That the named test was run and passed as written |
| MIL-STD-883 | Test methods for microcircuits | That the named method was applied to a microcircuit under its own conditions |
| MIL-STD-750 | Test methods for discrete semiconductor devices | That a discrete device came through the named procedure |
| MIL-PRF-38534 | Performance specification for hybrid microcircuits | The reference cited when an assembly is announced as built to a hybrid standard |
What do the cited tests actually exercise?
The tests quoted most often in these families are thermal cycling, mechanical shock, vibration, hermeticity in its fine and gross forms, electrical burn-in and visual inspection. What each one exercises is written in the method, not in the name of the test.
No cycle count and no temperature belong to the family itself. Both are set by the method selected and by the level requested, which is why a datasheet that quotes the test without the condition is quoting half a sentence. The other half sits in the document, and it is what decides whether two parts claiming the same test were ever asked the same question.
Screening is not a service prediction
A part can pass every method it is cited against and still be the wrong part for a circuit. Screening asks whether the package survives a defined stress. It does not ask how insertion loss and isolation behave across a band, how a driver clears the stored charge of a diode, or what a junction tolerates when RF power is present during the switching event. Those are electrical questions, answered by measurement, on a bench whose calibration needs the same discipline as a screening run.
The reading habit is the same on that side of the page. A figure quoted to a tenth of a decibel out of a bench whose calibration is not qualified is not wrong; it is unqualified. A screening line and a measurement line are two citations of two kinds of document, and neither substitutes for the other.
How should a screening line be read?
In order, and with the document open. The line carries a family, a number and sometimes a level; everything that gives those three their meaning sits elsewhere, and the reading is a matter of going to fetch it before the comparison rather than after it.
Reading a screening line in order
- Note the family and the method number separately, and identify which document the number is drawn from.
- Read the conditions in that document: profile, duration, levels and acceptance criteria, in the wording the method uses.
- Check whether the line quotes a level. Where it does not, the level comes from the method, not from a choice made for the part.
- Keep what was screened apart from what was measured. A screening result is not an electrical figure.
- Treat a line with no method number as missing information, not as a house style.
- Record the revision of the document you read, since a citation outlives the edition it pointed at.
Common mistakes
- Reading a screening line as a statement about service life. The method certifies the test, not the years.
- Comparing two parts on the name of a test alone when the cited numbers come from different families.
- Assuming a cycle count or a temperature from the family name. Both depend on the method and the level requested.
- Folding the electrical figures into the screening claim, as though a screened part were automatically the better measured part.
- Taking a citation of the hybrid specification as a performance claim rather than as a statement about how the assembly was built and documented.
What to do with the number, once read
The step is short, and it belongs before any comparison. Open the method document behind every screening line on the page and write down, for each one, the profile, the duration and the acceptance criterion in the method’s own words. Then set the datasheets side by side again. What has changed is not the parts; it is the question each line was actually asked.
The same reading carries one level up, to what an assembly integrates, where a citation of the hybrid specification is often the only sentence on the page about how the hardware inside was put together. How this publication reads a datasheet, and where its figures come from, is set out in sources and method.